Revert r330897:

This was intended to be a non-functional change. It wasn't. The commit
message was thus wrong. In addition it broke arm, and merged crypto
related code.

Revert with prejudice.

This revert skips files touched in r316370 since that commit was since
MFCed. This revert also skips files that require $FreeBSD$ property
changes.

Thank you to those who helped me get out of this mess including but not
limited to gonzo, kevans, rgrimes.

Requested by: gjb (re)

Partial merge of the SPDX changes

These changes are incomplete but are making it difficult
to determine what other changes can/should be merged.

No objections from: pfg

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

CALLOUT_MPSAFE has lost its meaning since r141428, i.e., for more than ten
years for head. However, it is continuously misused as the mpsafe argument
for callout_init(9). Deprecate the flag and clean up callout_init() calls
to make them more consistent.

Differential Revision: https://reviews.freebsd.org/D2613
Reviewed by: jhb
MFC after: 2 weeks

Add 32-bit support for Gxemul's oldtestmips machine emulation

Original work by: kan@

Use MIPS_PHYS_TO_DIRECT_UNCACHED rather than a homegrown version which is not
compatible with 32-bit kernels.

In the gxemul console, check the RB_SERIAL boot flag, and change the
relative priority of the gxemul console in line with its role as a
"seiral console". This allows it to override video console drivers
that might otherwise take precdence, subject to that boot flag.

Sponsored by: DARPA, AFRL

Rename the gxemul console device to "ttyu0" to match the expectations of
the default MIPS /etc/ttys.

Sponsored by: DARPA, AFRL

Merge a rudimentary gxemul "oldtestmips" port. This consists almost
entirely of one machdep file lifted from the MALTA port, as well as
a low-level console and tty driver for the gxemul debugging console
device (the emulators stdio). As with many low-level embedded and
hypervisor console devices, it is polled only, so we drive TTY I/O
from a callout; we are perhaps a bit too aware of the MIPS physical
maps in order to attach the console before newbus comes to life.

The sample kernel configuration depends on an MD-based root file
system, which is not provided. However, any 64-bit, big-endian
userspace image (such as one generated for MALTA) should work.

This will hopefully be supplemented by additional device drivers for
gxemul-specific hardware simulations from Juli Mallett. We have
found oldtestmips quite useful for testing and improving aspects of
the MIPS port, so it's worth supporting better in FreeBSD.

Requested by: theraven, jmallett
Sponsored by: DARPA, AFRL
MFC after: 3 weeks