perf, x86: Provide means for disabling userspace RDPMC

Allow the disabling of RDPMC via a pmu specific attribute:

  echo 0 > /sys/bus/event_source/devices/cpu/rdpmc

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Cc: Arun Sharma <asharma@fb.com>
Link: http://lkml.kernel.org/n/tip-pqeog465zo5hsimtkfz73f27@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 02545e6..5311b79 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -615,6 +615,7 @@
 	struct list_head		entry;
 
 	struct device			*dev;
+	const struct attribute_group	**attr_groups;
 	char				*name;
 	int				type;