Support AArch64 FreeBSD VMs

[emaste]

Description

Add FreeBSD/arm64 VM instances.

Context

We have an interest in building and testing FreeBSD itself, as well as downstream projects, on AArch64/arm64. Downstream projects of particular interest are languages, runtimes, and toolchains (go, jdk, python, etc.)

Anything Else

FreeBSD provides AWS VM images for Graviton instances.

Some links:

• https://aws.amazon.com/about-aws/whats-new/2021/02/aws-graviton2-based-m6g-c6g-r6g-instances-available-additional-regions/
• https://klarasystems.com/articles/the-next-level-freebsd-on-arm64-in-the-cloud/