timekeeping: Add CLOCK_TAI clockid

This add a CLOCK_TAI clockid and the needed accessors.

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>
diff --git a/include/linux/time.h b/include/linux/time.h
index 47210a1..22d81b3 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -183,6 +183,7 @@
 extern int timekeeping_inject_offset(struct timespec *ts);
 extern s32 timekeeping_get_tai_offset(void);
 extern void timekeeping_set_tai_offset(s32 tai_offset);
+extern void timekeeping_clocktai(struct timespec *ts);
 
 struct tms;
 extern void do_sys_times(struct tms *);