selftests/powerpc/pmu: Add selftest to check PERF_SAMPLE_REGS_INTR option will not...

selftests/powerpc/pmu: Add selftest to check PERF_SAMPLE_REGS_INTR option will not crash on any platforms

With sampling, --intr-regs option is used for capturing
interrupt regs. When --intr-regs option is used, PMU code
uses is_sier_available() function which uses PMU flags in
the code. In environment where platform specific PMU is
not registered, PMU flags is not defined. A fix was added
in kernel to address crash while accessing is_sier_available()
function when pmu is not set. commit 6d2cbbc46623 ("powerpc/perf:
Fix crash with is_sier_available when pmu is not set").

Add perf sampling test to exercise this code and make sure
enabling intr_regs shouldn't crash in any platform. Testcase
uses software event cycles since software event will work even
in cases without PMU.

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/20220610134113.62991-12-atrajeev@linux.vnet.ibm.com