arm_mpam: Disable preemption when making accesses to fake MSC in kunit test

arm_mpam: Disable preemption when making accesses to fake MSC in kunit test

Accesses to MSC must be made from a cpu that is affine to that MSC and the
driver checks this in __mpam_write_reg() using smp_processor_id(). A fake
in-memory MSC is used for testing. When using that, it doesn't matter which
cpu we access it from but calling smp_processor_id() from a preemptible
context gives warnings when running with CONFIG_DEBUG_PREEMPT.

Add a test helper that wraps mpam_reset_msc_bitmap() with preemption
disabled to ensure all (fake) MSC accesses are made with preemption
disabled.

Signed-off-by: Ben Horgan <ben.horgan@arm.com>
Reviewed-by: James Morse <james.morse@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>