time: More core infrastructure for timespec64

Helper and conversion functions for timespec64.

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

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

diff --cc include/linux/time64.h
Simple merge

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