perf powerpc: Add support for PERF_SAMPLE_WEIGHT_STRUCT

Add arch specific arch_evsel__set_sample_weight() to set the new
sample type for powerpc.

Add arch specific arch_perf_parse_sample_weight() to store the
sample->weight values depending on the sample type applied.
if the new sample type (PERF_SAMPLE_WEIGHT_STRUCT) is applied,
store only the lower 32 bits to sample->weight. If sample type
is 'PERF_SAMPLE_WEIGHT', store the full 64-bit to sample->weight.

Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Reviewed-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Link: https://lore.kernel.org/r/1616425047-1666-4-git-send-email-atrajeev@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>