scsi: ufs: add support to power collapse UFS host controller

If UFS link is in OFF state then UFS host controller can be power collapsed
to avoid leakage current from it. Note that if UFS host controller is power
collapsed, full UFS reinitialization will be required on resume to
re-establish the link between host and device.

Change-Id: I7b96c65360f170eed5f063b1645bed149b363997
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>