timekeeping: Move TAI managment into timekeeping core from ntp

Currently NTP manages the TAI offset. Since there's plans for a
CLOCK_TAI clockid, push the TAI management into the timekeeping
core.

CC: Thomas Gleixner <tglx@linutronix.de>
CC: Eric Dumazet <eric.dumazet@gmail.com>
CC: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>

include/linux/timekeeper_internal.h

@@ -62,6 +62,9 @@ struct timekeeper {
 	ktime_t			offs_boot;
 	/* The raw monotonic time for the CLOCK_MONOTONIC_RAW posix clock. */
 	struct timespec		raw_time;
+	/* The current UTC to TAI offset in seconds */
+	s32			tai_offset;
+
 	/* Seqlock for all timekeeper values */
 	seqlock_t		lock;
 };