perf tools: Add stat config user level event

Adding the stat config event to pass/store stat config data, so report
tools (report/script) know how to interpret stat data.

The config data is stored in a 'tag|value' way to allow for easy
extension and backwards compatibility.

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/1445784728-21732-12-git-send-email-jolsa@kernel.org


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