perf timechart: Adjust perf timechart to the new power events

builtin-timechart must only pass -e power:xy events if they are supported by
the running kernel, otherwise try to fetch the old power:power{start,end}
events.

For this I added the tiny helper function:

   int is_valid_tracepoint(const char *event_string)

to parse-events.[hc], which could be more generic as an interface and support
hardware/software/... events, not only tracepoints, but someone else could
extend that if needed...

Signed-off-by: Thomas Renninger <trenn@suse.de>
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
Acked-by: Jean Pihet <j-pihet@ti.com>
LKML-Reference: <1294073445-14812-4-git-send-email-trenn@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

tools/perf/util/parse-events.h

@@ -36,6 +36,7 @@ extern int parse_filter(const struct option *opt, const char *str, int unset);
 #define EVENTS_HELP_MAX (128*1024)
 
 extern void print_events(void);
+extern int is_valid_tracepoint(const char *event_string);
 
 extern char debugfs_path[];
 extern int valid_debugfs_mount(const char *debugfs);