selftests/powerpc/pmu: Add selftest to check constraint for number of counters in use.

Testcase for group constraint check for number of counters in use. The
number of programmable counters is from PMC1 to PMC4. Testcase uses four
events with PMC1 to PMC4 and 5th event without any PMC which is expected
to fail since it is exceeding the number of counters in use.

Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220610134113.62991-19-atrajeev@linux.vnet.ibm.com