scsi: ufs: do clock gating only after hibern8

Clock gating work must be executed only after auto hibern8
timeout has expired in the hardware or after aggressive
hibern8 on idle software timeout. Using jiffy based low
resolution delayed work is not reliable to guarantee this,
hence use a high resolution timer to make sure we schedule
the gate work precisely more than hibern8 timeout.

Change-Id: Ib2119bc58a1cdb7a5908db1b8775cb4f13db18f7
Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>