perf stat: Update POWER9 metrics to utilize other metrics

perf stat: Update POWER9 metrics to utilize other metrics

These changes take advantage of the new capability added in merge commit
5ffeae2bb2956963acb1be52c5e680e35d65396a "Allow using computed metrics
in calculating other metrics".

The net is a simplification of the expressions for a handful of metrics,
but no functional change.

Signed-off-by: Paul Clarke <pc@us.ibm.com>
Reviewed-by: Kajol Jain <kjain@linux.ibm.com>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: http://lore.kernel.org/lkml/20200813222155.268183-1-pc@us.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>