powerpc/perf: Use PM_INST_DISP for generic instructions sample

Since PM_INST_CMPL may not provide right counts in all
sampling scenarios in power9 DD1, instead use PM_INST_DISP.
Patch also update generic instruction sampling with the same.

Signed-off-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>