arm64: Hyper-V: enablement for ARM64 in Hyper-V (Part 3, final)

This is the last part for ARM64 Hyper-V enablement. This includes
commone files and make file changes to enable the ARM64 FreeBSD
guest on Hyper-V. With this patch, it should be able to build
the ARM64 image and install it on Hyper-V.

Reviewed by: emaste, andrew, whu
Tested by: Souradeep Chakrabarti <schakrabarti@microsoft.com>
Sponsored by: Microsoft
Differential Revision: https://reviews.freebsd.org/D36744