Testing Armv8-R

[jonathanpallant]

We currently cannot test Armv8-R because Cortex-R52 support (the only Armv8-R CPU) was added in QEMU 9, and the Github ubuntu runners don't have it, and it's not easily available for download as a binary package.

When we do, we should copy some of the versatileab tests over to MPS3-AN536, like for data aborts and prefetch aborts.