scsi: ufs: add checks before setting hibern8/clk-gating on idle states

"Hibern8 on idle" and "Clock gating on idle" features can be turned
on/off selectively which means their state information is only important
if that particular feature is enabled. This change makes sure that we only
look at state of these features if feature itself is enabled.

Change-Id: I25ef3d9dd60e69afe3f2d9dce602ae48f1b4a044
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>