perf ui/tui: Add 'F' hotkey to toggle percentage output

Add 'F' hotkey to toggle relative and absolute percentage of filtered
entries.

Suggested-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/1397145720-8063-7-git-send-email-namhyung@kernel.org


Signed-off-by: Jiri Olsa <jolsa@redhat.com>