MFC r335030:

Add SPDX tags to vmm(4).

Sponsored by: iXsystems Inc.

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

Don't require <sys/cpuset.h> to be always included before <machine/vmm.h>.

Only a subset of source files that include <machine/vmm.h> need to use the
APIs that require the inclusion of <sys/cpuset.h>.

MFC after: 1 week

Change the type of the first argument to the I/O emulation handlers to
'struct vm *'. Previously it used to be a 'void *' but there is no reason
to hide the actual type from the handler.

Discussed with: tychon
MFC after: 1 week

Move the ACPI PM timer emulation into vmm.ko.

This reduces variability during timer calibration by keeping the emulation
"close" to the guest. Additionally having all timer emulations in the kernel
will ease the transition to a per-VM clock source (as opposed to using the
host's uptime keep track of time).

Discussed with: grehan