selftest/powerpc: Add PAPR sysfs attributes sniff test

Include a testcase to check if the sysfs files for energy and frequency
related have its related attribute files exist and populated

Signed-off-by: Pratik R. Sampat <psampat@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220217105321.52941-3-psampat@linux.ibm.com