KVM: selftests: aarch64: vPMU register test for unimplemented counters

Add a new test case to the vpmu_counter_access test to check
if PMU registers or their bits for unimplemented counters are not
accessible or are RAZ, as expected.

Signed-off-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20231020214053.2144305-12-rananta@google.com
[Oliver: fix issues relating to exception return address]
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>