timer: Added usleep[_range] timer

usleep[_range] are finer precision implementations of msleep
and are designed to be drop-in replacements for udelay where
a precise sleep / busy-wait is unnecessary. They also allow
an easy interface to specify slack when a precise (ish)
wakeup is unnecessary to help minimize wakeups

As ACK'd upstream:
https://patchwork.kernel.org/patch/112813/



Change-Id: I277737744ca58061323837609b121a0fc9d27f33
Signed-off-by: Patrick Pannuto <ppannuto@codeaurora.org>
(cherry picked from commit 08c118890b06595dfc26d47ee63f59e73256c270)

Conflicts:

	include/linux/delay.h
	kernel/timer.c