perf tools: Add stat events fprintf functions

perf tools: Add stat events fprintf functions

Introducing the following functions to display the stat events for raw
dump.

  perf_event__fprintf_stat
  perf_event__fprintf_stat_round
  perf_event__fprintf_stat_config

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Kan Liang <kan.liang@intel.com>
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/1445784728-21732-20-git-send-email-jolsa@kernel.org
[ s/stat/st/g and s/round/rd/g parameters to fix 'already defined' build error with older distros (e.g. RHEL6.7) ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>