bhyvectl: Add arm64 bits and hook it up to the build

For now this implementation doesn't provide any machine dependent
functionality on arm64, but it's enough to be able to reset and destroy
VMs.

Reviewed by: jhb
Sponsored by: Innovate UK
Differential Revision: https://reviews.freebsd.org/D44932

arm64: Connect bhyve and libvmmapi to the build

Reviewed by: corvink, andrew, jhb, emaste
MFC after: 2 weeks
Sponsored by: Innovate UK
Differential Revision: https://reviews.freebsd.org/D41742

ofwdump: install dependent on MK_FDT

The utility depends on the presence of the openfirm(4) pseudo-device,
which is gated by the FDT kernel option. The MK_FDT knob is correctly
set to "yes" for FDT/OFW-enabled platforms (powerpc* included); use it
to install the utility and eliminate the arch-specific Makefile logic.

No functional change intended.

Reviewed by: emaste, pkubaj
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D41977

Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

Fix the name of Makefile.aarch64

Makefile.arm64 relies on being included via Makefile.${MACHINE}. This
only works when arm64 is the only aarch64 architecture. Switch to
Makefile.aarch64 so downstream CheriBSD can use the file when building
for Morello which uses a differen ${MACHINE} value.

Sponsored by: Innovate UK