perf tools: Introduce trace_event__tp_format_id()

To get struct event_format object from tracepoint ID.  It will be used
in following patches.

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/1468148882-10362-3-git-send-email-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/trace-event.c

@@ -105,3 +105,11 @@ trace_event__tp_format(const char *sys, const char *name)
 
 	return tp_format(sys, name);
 }
+
+struct event_format *trace_event__tp_format_id(int id)
+{
+	if (!tevent_initialized && trace_event__init2())
+		return ERR_PTR(-ENOMEM);
+
+	return pevent_find_event(tevent.pevent, id);
+}