perf script: Add --show-round-event to display PERF_RECORD_FINISHED_ROUND

perf script: Add --show-round-event to display PERF_RECORD_FINISHED_ROUND

Adding --show-round-event to display PERF_RECORD_FINISHED_ROUND events
like:

  # perf script --show-round-events 2>/dev/null
               yes  8591 [002] 124177.397597:         18         cpu/mem-stores/P: ff...
               yes  8591 [002] 124177.397615:          1 cpu/mem-loads,ldlat=30/P: ff...
  PERF_RECORD_FINISHED_ROUND
              perf 10380 [001] 124177.397622:          6 cpu/mem-loads,ldlat=30/P: ff...
  PERF_RECORD_FINISHED_ROUND
           swapper     0 [000] 124177.400518:         88         cpu/mem-stores/P: ff...
           swapper     0 [000] 124177.400521:         88         cpu/mem-stores/P: ff...

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20180206181813.10943-4-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>