scsi: ufs: add support for low voltage VCC support

UFS3.0 devices are capable of running at lower level (2.5v) of VCC rail.
If both host and device supports 2.5v level then we do runtime switch
of UFS VCC voltage level.

Change-Id: Ifa7f73f6afdfc382fa018c7403a2da79d08df845
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>