perf trace: Sort summary output by number of events

perf trace: Sort summary output by number of events

  # trace -a -s sleep 1 |& grep events | tail
   gmain (1733), 34 events, 1.0%, 0.000 msec
   hexchat (9765), 46 events, 1.4%, 0.000 msec
   ssh (11109), 80 events, 2.4%, 0.000 msec
   sleep (32631), 81 events, 2.4%, 0.000 msec
   qemu-system-x86 (10021), 272 events, 8.2%, 0.000 msec
   Xorg (1965), 322 events, 9.7%, 0.000 msec
   SoftwareVsyncTh (10922), 366 events, 11.1%, 0.000 msec
   gnome-shell (2231), 446 events, 13.5%, 0.000 msec
   qemu-system-x86 (9931), 468 events, 14.1%, 0.000 msec
   firefox (10871), 1098 events, 33.2%, 0.000 msec
  [root@jouet ~]#

Suggested-by: Milian Wolff <milian.wolff@kdab.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-ye4cnprhfeiq32ar4lt60dqs@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>