scsi: ufs: reduce the interrupts for power mode change requests

DME commands such as Hibern8 enter/exit and gear switch generate 2
completion interrupts, one for confirmation that command is received
by local UniPro and 2nd one is the final confirmation after communication
with remote UniPro. Currently both of these completions are registered
as interrupt events which is not quite necessary and instead we can
just wait for the interrupt of 2nd completion, this should reduce
the number of interrupts and could reduce the unnecessary CPU wakeups
to handle extra interrupts.

Change-Id: I5365b8b5cae952fd4bd7bb93cca0cfe76ea8b619
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>