perf bench: List output formatting options on 'perf bench -h'

So 'perf bench -h' is not very helpful when printing the help line
about the output formatting options:

    -f, --format <default>
                              Specify format style

There are two output format styles, 'default' and 'simple', so improve
the help text to:

    -f, --format <default|simple>
                              Specify the output formatting style
Signed-off-by: NIngo Molnar <mingo@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1445241870-24854-7-git-send-email-mingo@kernel.org
[ Removed leftovers from the mem-functions.c rename ]
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-bench.c

@@ -110,7 +110,7 @@ int bench_format = BENCH_FORMAT_DEFAULT;
 unsigned int bench_repeat = 10; /* default number of times to repeat the run */
 
 static const struct option bench_options[] = {
-	OPT_STRING('f', "format", &bench_format_str, "default", "Specify format style"),
+	OPT_STRING('f', "format", &bench_format_str, "default|simple", "Specify the output formatting style"),
 	OPT_UINTEGER('r', "repeat",  &bench_repeat,   "Specify amount of times to repeat the run"),
 	OPT_END()
 };