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

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

Respect the destination operand size of the 'Input from Port' instruction.

Approved by: grehan (co-mentor)

Add support for reading the PIT Counter 2 output signal via the NMI
Status and Control register at port 0x61.

Be more conservative about "catching up" callouts that were supposed
to fire in the past by skipping an interrupt if it was
scheduled too far in the past.

Restore the PIT ACPI DSDT entries and add an entry for NMISC too.

Approved by: neel (co-mentor)

Move the atpit device model from userspace into vmm.ko for better
precision and lower latency.

Approved by: grehan (co-mentor)