perf top: Support --group-sort-idx to change the sort order

perf top: Support --group-sort-idx to change the sort order

'perf report' supports the option --group-sort-idx, which sorts the
output by the event at the index n in event group.

For example:

  perf record -e cycles,instructions,cache-misses
  perf report --group --group-sort-idx 2 --stdio

The perf-report output is sorted by cache-misses.

This patch supports --group-sort-idx in perf-top.

For example:

  perf top --group -e cycles,instructions,cache-misses --group-sort-idx 2

The perf-top output is sorted by cache-misses.

Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Suggested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jin Yao <yao.jin@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20200324220711.6025-1-yao.jin@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>