MFC r325834,r325997,326502: Move sys/boot to stand/

This is effectively a direct commit to stable/11, due to differences between
stable/11 and head. Changes to DTS in sys/boot/fdt/dts were often
accompanied by kernel changes. Many of these were also risc-v updates that
likely had many more dependencies to MFC.

Because of this, sys/boot/fdt/dts remains as-is while everything else in
sys/boot relocates to stand/.

r325834: Move sys/boot to stand. Fix all references to new location

r325997: Remove empty directories.

r326502: Document the sys/boot -> stand move in hier.7 and the top-level README.

MFC Loader Fixes 2017q1: r311458,r312237,r312314,r312374,r312947,r313042,
r313047,r313166,r313328,r313332,r313333,r313337,r313348,r313349,r313389,
r313442,r313451,r313575,r313645,r313710,r314114,r314213,r314275,r314945,
r314948,r315008,r315408,r315427,r315645,r315646,r315648,r315653,r315850,
r316064,r316078,r316079,r316100,r316104,r316111,r316112,r316171,r316279,
r316280,r316287,r316311,r316343,r316424,r316436

r311458: Use compiler driver to link BERI boot loaders

r312237: loader.efi: find_currdev() can leak memory

r312314: loader: move device path definitions to include/efidevp.h

r312374: loader: efi devpath api usage should be more aware of NULL pointers

r312947: Remove "-Xassembler -G0" from CFLAGS.

r313042: loader.efi environment related cleanups

r313047: loader: disk/part api needs to use uint64_t offsets

r313166: loader: libefi/env.c warnings in arm build

r313328: loader: Implement disk_ioctl() to support DIOCGSECTORSIZE and
DIOCGMEDIASIZE.

r313332: loader: bcache read ahead block count should take account the large
sectors

r313333: loader: Replace EFI part devices.

r313337: loader: 313329 missed ZFS guard in loader/main.c

r313348: loader: biosdisk fix for 2+TB disks

r313349: loader: disk io should not use alloca()

r313389: efipart is also using the '%S' printf format, add -Wno-format for
it.

r313442: loader: possible NULL pointer dereference in efipart.c

r313451: loader: possible NULL pointer dereference in bcache.c

r313575: makefs: make the buffer functions look exactly like the kernel ones

r313645: loader: implement MEDIA_FILEPATH_DP support in efipart

r313710: loader: cstyle fixes and DIOCGMEDIASIZE should use uint64_t

r314114: Use LDFLAGS with CC instead of _LDFLAGS.

r314213: Remove control+r handling from geliboot's pwgets()

r314275: Remove unused macro from common/drv.c.

r314945: Some style(9) fixes. No functional changes.

r314948: Try to extract the RFC1048 data from PXE.

r315008: r314948 seems to be missing a variable or two that will break

r315408: loader: remove open_disk cache

r315427: loader: biosdisk should report IO error from INT13

r315645: loader: disk_cleanup was left in userboot_disk.c

r315646: loader: pxe.h constants have wrong values

r315648: libstand: verify value provided by nfs.read_size

r315653: loader: verify the value from dhcp.interface-mtu and use snprintf
o set mtu

r315850: The original author abused Nd (one-line description, used by
makewhatis)

r316064: Fix build with path names with 'align' or 'nop' in them.

r316078: gpt*boot: Save a bit more memory when LOADER_NO_GELI_SUPPORT is
specified

r316079: Simply retire the sedification of the boot2.s file.

r316100: Remove -fno-guess-branch-probability and -fno-unit-at-a-time.

r316104: Use `NO_WCAST_ALIGN` instead of spelling it out as -Wno-cast-align
in CFLAGS

r316111: loader: move bios getsecs into time.c

r316112: loader: ls command should display file types properly

r316171: xfsread inlined uses more space, so remove the inline tag.

r316279: loader: efipart should check disk size from partition table

r316280: loader: simplify efi_zfs_probe and avoid double probing for zfs.

r316287: Remove OLD_NFSV2 from loader and libstand

r316311: Add explicit_bzero() to libstand, and switch GELIBoot to using it

r316343: Implement boot-time encryption key passing (keybuf)

r316424: Fix sparc64 build broken by r316343 and r316076

r316436: Restore EFI boot environment functionality broken in r313333

PR: 216940 217298 217935

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Make the RTC checking for QEMU even more aggressive.

At work, where we use use KVM+QEMU, we notice that pxeboot is pratically
impossible because of network timeouts. This is due to the fact that the
RTC code makes aggressive jumps.

Two RTC reads does not seem to be sufficient. Change the code to check
for 8 identical RTC values.

Sponsored by: Kumina bv

Implement a workaround for a long-standing problem in
libi386's time(), caused by a qemu bug. The bug might
be present in other BIOSes, too.

qemu either does not simulate the AT RTC correctly or
has a broken BIOS 1A/02 implementation, and will return
an incorrect value if the RTC is read while it is being
updated.

The effect is worsened by the fact that qemu's INT 15/86
function ("wait" a.k.a. usleep) is non-implmeneted or
broken and returns immediately, causing beastie.4th to
spin in a tight loop calling the "read RTC" function
millions of times, triggering the problem quickly.

Therefore, we keep reading the BIOS value until we get
the same result twice. This change fixes beastie.4th's
countdown under qemu.

Approved by: des (mentor)

Use __FBSDID().
Also some minor copyright style cleanups.

Cleanup warnings. Most of these are signed/unsigned warnings, as well as
some added const's.

Substantially revamp the way that we determine the amount of memory available
for our use. Use the same search order for BIOS memory size functions
as the kernel will later use.

Allow the loader to use all of the detected physical memory (this will
greatly help people trying to load enormous memory disk images).

More correctly handle running out of memory when loading an object.

Use the end of base memory for the top of the heap, rather than
blindly hoping that there is 384k left.

Add copyrights to a couple of files I forgot.

Fix comment to match code

Initial integration of the i386 bootloader and BTX.

- Discard large amounts of BIOS-related code in favour of the more compact
BTX vm86 interface.
- Build the loader module as ELF, although the resulting object is a.out,
make gensetdefs 32/64-bit sensitive and use a single copy of it.
- Throw away installboot, as it's no longer required.
- Use direct bcopy operations in the i386_copy module, as BTX
maps the first 16M of memory. Check operations against the
detected size of actual memory.