ANDROID: KVM: arm64: Add S2MPU kselftest

Add a kselftest which exercises the S2MPU's MPT logic. The functions are
included into a kernel module and exercised in EL1. This is because
testing the EL2 driver itself would require generating DMA traffic and
probing the S2MPU without crashing the system. Instead, the logic is
used on a local FMPT/SMPT and the results are inspected.

Test: run kvm/aarch64/s2mpu kselftest
Bug: 190463801
Signed-off-by: David Brazdil <dbrazdil@google.com>
Change-Id: Ib1e572e3247d864e59fad8a4960e38956237ef8c