hrtimer: reorder struct hrtimer to save 8 bytes on 64bit builds

reorder struct hrtimer to save 8 bytes on 64 bit builds when
CONFIG_TIMER_STATS selected.  (also removes 8 bytes from signal_struct)
Signed-off-by: NRichard Kennedy <richard@rsk.demon.co.uk>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

include/linux/hrtimer.h

@@ -115,12 +115,12 @@ struct hrtimer {
 	enum hrtimer_restart		(*function)(struct hrtimer *);
 	struct hrtimer_clock_base	*base;
 	unsigned long			state;
-	enum hrtimer_cb_mode		cb_mode;
 	struct list_head		cb_entry;
+	enum hrtimer_cb_mode		cb_mode;
 #ifdef CONFIG_TIMER_STATS
+	int				start_pid;
 	void				*start_site;
 	char				start_comm[16];
-	int				start_pid;
 #endif
 };