selftests/powerpc/pmu: Add mask/shift bits for extracting threshold compare field

In power10, threshold compare field is not part of the raw event code
and provided via event attribute config1. Hence add the mask and shift
bits based on event attribute config1, to extract the threshold compare
value for power10

Also add a new function called get_thresh_cmp_val to compute and return
the threshold compare field for a given platform, since incase of
power10, threshold compare value provided is decimal.

Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220610134113.62991-2-atrajeev@linux.vnet.ibm.com