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: I6fea6c354cde5f7bd9d2a8a275c66e842726d358
Signed-off-by: Bao D. Nguyen <nguyenb@codeaurora.org>