timekeeping: Move lock out of timekeeper struct

Make the lock a separate entity. Preparatory patch for shadow
timekeeper structure.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[Merged with CLOCK_TAI changes]
Signed-off-by: John Stultz <john.stultz@linaro.org>

include/linux/timekeeper_internal.h

@@ -67,8 +67,6 @@ struct timekeeper {
 	/* Offset clock monotonic -> clock tai */
 	ktime_t			offs_tai;
 
-	/* Seqlock for all timekeeper values */
-	seqlock_t		lock;
 };
 
 static inline struct timespec tk_xtime(struct timekeeper *tk)