freezer: replace msleep with usleep_delay for sleep time of <20mS

usleep_delay() works more accurately for sleep time of <20mS.
All tasks can easily be frozen in under 10 ms, switch to using
an initial 1 ms sleep followed by exponential backoff until 8 ms.

Change-Id: Id932d7dbefe9c59eded33aa87cdb3cb8b581efa2
Signed-off-by: Sravan Kumar Ambapuram <asravan@codeaurora.org>