Introduce Armv8-R64 architecture and fvp-baser-aemv8r product
A set of commits to:
- Introduce support for the subset of the AArch64 architecture required for Armv8-R64, including the armv8r_mpu module.
- Introduce the fvp-baser-aemv8r product as a validation target.
GIC/interrupt support will be implemented in a future MR (the functions are stubs here).