perf annotate: Display percent type in stdio output

In following patches we will allow to switch percent type even for stdio
annotation outputs. Adding the percent type value into the annotation
outputs title.

  $ perf annotate --stdio
   Percent         |      Sou ... instructions:u } (2805 samples, percent: local period)
  --------------------------- ... ------------------------------------------------------
  ...

  $ perf annotate --stdio2
  Samples: 2K of events 'anon ...  count (approx.): 156525487, [percent: local period]
  safe_write.c() /usr/bin/yes
  Percent
  ...

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>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/20180804130521.11408-19-jolsa@kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>