timekeeping: Provide timespec64 based interfaces

To convert callers of the core code to timespec64 we need to provide
the proper interfaces.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Stultz <john.stultz@linaro.org>

diff --cc include/linux/timekeeping.h
Simple merge

diff --cc kernel/time/ntp.c
Simple merge

diff --cc kernel/time/timekeeping.c
Simple merge