KVM: arm64: Enforce reserved bits for PSCI target affinities

According to the PSCI specification, ARM DEN 0022D, 5.1.4 "CPU_ON", the
CPU_ON function takes a target_cpu argument that is bit-compatible with
the affinity fields in MPIDR_EL1. All other bits in the argument are
RES0. Note that the same constraints apply to the target_affinity
argument for the AFFINITY_INFO call.

Enforce the spec by returning INVALID_PARAMS if a guest incorrectly sets
a RES0 bit.

Signed-off-by: Oliver Upton <oupton@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210818202133.1106786-4-oupton@google.com