powerpc/perf: init pmu from core-book3s

Currenty pmu driver file for each ppc64 generation processor
has a __init call in itself. Refactor the code by moving the
__init call to core-books.c. This also clean's up compat mode
pmu driver registration.

Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
[mpe: Use SPDX tag for license]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>