selftests/powerpc/pmu/: Add interface test for mmcr0_pmcjce field

The testcase uses event code 0x500fa ("instructions") to verify the
PMCjCE bit setting in Monitor Mode Control Register 0 (MMCR0). This bit
is expected to be set in MMCR0 when using Performance Monitor Counter
5 (PMC5). Checks if perf interface sets this bit correctly.

Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
[mpe: Add error checking, drop GET_MMCR_FIELD, add to .gitignore]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220127072012.662451-13-kjain@linux.ibm.com