selftests/powerpc/pmu: Add selftest for group constraint for unit and pmc field in p9

Unit and pmu bits in the event code is used to program unit and pmc
fields in Monitor Mode Control Register 1 (MMCR1). For power9 platform,
incase unit field value is within 6 to 9, one of the event in the group
should use PMC4. Otherwise event_open should fail for that group.

Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220610134113.62991-33-atrajeev@linux.vnet.ibm.com