trace: annotate bitfields in struct ring_buffer_event

This gets rid of a heap of false-positive warnings from the tracer
code due to the use of bitfields.

[rebased for mainline inclusion]
Signed-off-by: Vegard Nossum <vegard.nossum@gmail.com>

include/linux/ring_buffer.h

@@ -1,6 +1,7 @@
 #ifndef _LINUX_RING_BUFFER_H
 #define _LINUX_RING_BUFFER_H
 
+#include <linux/kmemcheck.h>
 #include <linux/mm.h>
 #include <linux/seq_file.h>
 
@@ -11,7 +12,10 @@ struct ring_buffer_iter;
  * Don't refer to this struct directly, use functions below.
  */
 struct ring_buffer_event {
+	kmemcheck_bitfield_begin(bitfield);
 	u32		type_len:5, time_delta:27;
+	kmemcheck_bitfield_end(bitfield);
+
 	u32		array[];
 };