Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

bhyve(8): Correct copyright boilerplate for r359950

Use the text from the canonical sys/copyright.h 2-clause FreeBSD License.

Reported by: grehan (thanks!)

bhyve(8): Add VM Generation Counter ACPI device

Add an implementatation of the 'Virtual Machine Generation ID' spec to
Bhyve. The spec provides a randomly generated GUID (at bhyve start) in
device memory, along with an ACPI device with _CID VM_Gen_Counter and ADDR
evaluating to a Package pointing at that GUID.

A GPE is defined which Notifies the ACPI Device when the generation changes
(such as when a snapshot is rolled back). At this time, Bhyve does not
support snapshotting, so the GPE is never actually raised.

Suggested by: rpokala
Discussed with: grehan
Differential Revision: https://reviews.freebsd.org/D23165