scsi: ufs: core power collapse after clock gating

Currently we power collapse UFS controller core only during runtime suspend
but we could also power collapse it during clock gating as power collapse
latencies are only few microseconds. This change adds this aggressive power
collapse to save power.

Change-Id: Id550bcbcd044670cec08a6abb7225cb9386993b5
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>