KVM: arm64: selftests: Add tests for MMIO external abort injection

Test that the plumbing exposed to userspace for injecting aborts in
response to unexpected MMIO works as intended in two different flavors:

 - A 'normal' MMIO instruction (i.e. ESR_ELx.ISV=1)

 - An ISV=0 MMIO instruction with/without KVM_CAP_ARM_NISV_TO_USER
   enabled

Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20241025203106.3529261-5-oliver.upton@linux.dev


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