Using QEMU / Unicorn to emulate SecureROM for QA / Testing

[rickmark]

In the Discord server, we've been discussing the idea of using Unicorn (which uses QEMU) to emulate the SecureROM payload, and therefore test that our code works without a device physically used for testing. This has the advantages of:

• Being possible to run on each checkin in the GitHub Actions environment
• Being possible to run on all supported SoCs without all hardware in the hands of any one person
• Being faster and less frustrating then using a physical device in tight work loops
• Being a general BAMF flex...

Because Unicorn does not provide hardware, we would have to specifically handle interrupts and MMIO for the USB controller.

QEMU and Unicorn currently puke due to a lack of support for arbitrary MSR (machine specific registers). This should be handled with QEMU / xnu-qemu-arm64 as a dependency