Adding processing of stat and stat round events.

The stat data com in stat events, using generic function
process_stat_round_event to store data under perf_evsel object.

The stat-round events comes each interval or as last event in non
interval mode. The function process_stat_round_event process stored data
for each perf_evsel object and print it out.

Committer note:

After this patch:

  $ perf stat record usleep 1

   Performance counter stats for 'usleep 1':

        0.498381  task-clock (msec)       #    0.571 CPUs utilized
               2  context-switches        #    0.004 M/sec
               0  cpu-migrations          #    0.000 K/sec
             149  page-faults             #    0.299 M/sec
       1,271,635  cycles                  #    2.552 GHz
         928,712  stalled-cycles-frontend #   73.03% frontend cycles idle
         663,286  stalled-cycles-backend  #   52.16% backend  cycles idle
         792,614  instructions            #    0.62  insns per cycle
                                          #    1.17  stalled cycles per insn
         136,850  branches                #  274.589 M/sec
   <not counted>  branch-misses            (0.00%)

     0.000873419 seconds time elapsed

  $
  $ perf stat report

   Performance counter stats for '/home/acme/bin/perf stat record usleep 1':

        0.498381  task-clock (msec)       #    0.571 CPUs utilized
               2  context-switches        #    0.004 M/sec
               0  cpu-migrations          #    0.000 K/sec
             149  page-faults             #    0.299 M/sec
       1,271,635  cycles                  #    2.552 GHz
         928,712  stalled-cycles-frontend #   73.03% frontend cycles idle
         663,286  stalled-cycles-backend  #   52.16% backend  cycles idle
         792,614  instructions            #    0.62  insns per cycle
                                          #    1.17  stalled cycles per insn
         136,850  branches                #  274.589 M/sec
   <not counted>  branch-misses            (0.00%)

     0.000873419 seconds time elapsed

  $
Reported-by: Kan Liang <kan.liang@intel.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1446734469-11352-16-git-send-email-jolsa@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>