selftests/powerpc/pmu: Add selftest for checking valid and invalid bhrb filter maps

For PERF_SAMPLE_BRANCH_STACK sample type, different branch_sample_type,
ie branch filters are supported. All the branch filters are not
supported in powerpc. Example, power10 platform supports any, ind_call
and cond branch filters. Whereas, it is different in power9. Testcase
checks event open for invalid and valid branch sample types. The branch
types for testcase are picked from "perf_branch_sample_type" in
perf_event.h

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/20220610134113.62991-13-atrajeev@linux.vnet.ibm.com