perf timechart: Adjust perf timechart to the new power events

commit 20c457b8587bee4644d998331d9e13be82e05b4c upstream.

[This patch is part of mainline git commit 20c457b8587bee4644d9.
  This should fix:
  http://www.mail-archive.com/linux-perf-users@vger.kernel.org/msg00057.html

  The regression was introduced by git commit:
  4c21adf26f8fcf86a755b9b9f55c2e9fd241e1fb]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>