libsa: Remove redundant sys/cdefs.h

Sponsored by: Netflix

Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

stand: Create common gen_setcurrdev and replace code

Replace 4 identical copies of *_setcurrdev with gen_setcurrdev to avoid
having to create a 5th copy. uboot_setcurrdev is actually different and
needs to remain separate (even though it's quite similar).

Sponsored by: Netflix
Reviewed by: fuz@fuz.su, kevans
Differential Revision: https://reviews.freebsd.org/D38003

stand/efi: Move to using common devparse()

We no longer need to have to hand-code this for each boot loader since
devparse() handles them all with dv_parsedev().

Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D37340

stand: Change zfs_parsedev() API

Change the first argument to zfs_parsedev() to be a pointer to a struct
devdesc *. This now gets filled in with a malloc'd structure that's
returned to the caller that the caller is repsonsible for freeing. Most
nplaces in the tree passed in a malloc'd pointer anyway, and this moves
knowledge of zfs_devdesc more firmly into the zfs.c code.

Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D37336

stand: Change disk_parsedev() API

Change the first argument to disk_parsedev() to be a pointer to a struct
devdesc *. This now gets filled in with a malloc'd structure that's
returned to the caller that the caller is repsonsible for freeing. Most
places in the tree passed in a malloc'd pointer anyway, and this moves
knowledge of disk_devdesc more firmly into the disk.[ch] code.

Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D37335

stand: efi_fmtdev can be reduced to devformat

devformat produces the same output as efi_fmtdev, so just use it to
reduce on the dependencies.

Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D35924

loader: implement mount/unmount rootfs

We want to keep our root file system open to preserve bcache segment
between file accesses, thus reducing physical disk IO.

Reviewed by: imp, allanjude, kevans (previous version)
Differential Revision: https://reviews.freebsd.org/D30848
MFC after: 1 month

Start to reduce the number of #ifdef EFI_ZFS_BOOT

There's a number of EFI_ZFS_BOOT #ifdefs that aren't needed, or can be
eliminated with some trivial #defines. Remove the EFI_ZFS_BOOT ifdefs
that aren't needed. Replace libzfs.h include which is not safe to
include without EFI_ZFS_BOOT with efizfs.h which is and now
conditionally included libzfs.h. Define efizfs_set_preferred away
and define efi_zfs_probe to NULL when ZFS is compiled out.

Remove d_type from devdesc. It's not needed as we can fetch it from
d_dev->dv_type when we need it.

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

Sponsored by: Netflix