perf tools: Add an option to multiplex counters in a single channel

Add an option to multiplex counters output in the channel of
the group leader, ie: the first counter opened:

	-M --multiplex

The effect is better serialized samples. This is especially
useful for tracepoint samples that need to be well serialized
for their post-processing.

Also make use of this option in 'perf sched'.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

tools/perf/builtin-sched.c

@@ -1660,6 +1660,8 @@ static const char *record_args[] = {
 	"record",
 	"-a",
 	"-R",
+	"-M",
+	"-g",
 	"-c", "1",
 	"-e", "sched:sched_switch:r",
 	"-e", "sched:sched_stat_wait:r",