Continuing aarch64/arm64 Issues with QEMU static

This is a follow-on to #240 which is still not fixed after PR #251.  On aarch64/arm64 platforms, the logic in `custompios` is still trying to use `qemu-aarch64-static` unnecessarily. Part of my original patch didn't make it into PR #251.

https://github.com/guysoft/CustomPiOS/pull/261