time: Provide y2038 safe timekeeping_inject_sleeptime() replacement

As part of addressing "y2038 problem" for in-kernel uses, this
patch adds timekeeping_inject_sleeptime64() using timespec64.

After this patch, timekeeping_inject_sleeptime() is deprecated
and all its call sites will be fixed using the new interface,
after that it can be removed.

NOTE: timekeeping_inject_sleeptime() is safe actually, but we
want to eliminate timespec eventually, so comes this patch.

Signed-off-by: pang.xunlei <pang.xunlei@linaro.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>