powerpc/perf: Refactor the code definition of perf reg extended mask

PERF_REG_PMU_MASK_300 and PERF_REG_PMU_MASK_31 defines the mask
value for extended registers. Current definition of these mask values
uses hex constant and does not use registers by name, making it less
readable. Patch refactor the macro values by or'ing together the actual
register value constants. Also include PERF_REG_EXTENDED_MAX as
part of enum definition.

Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Reviewed-by: Kajol <Jain&lt;kjain@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211007065505.27809-2-atrajeev@linux.vnet.ibm.com