KVM: arm64: selftests: Catch up set_id_regs with the kernel

Add test coverage for ID_AA64MMFR3_EL1 and the recently added
FEAT_DoubleFault2.

Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250708172532.1699409-28-oliver.upton@linux.dev


Signed-off-by: Oliver Upton <oliver.upton@linux.dev>