scsi: ufs: optimize system suspend handling

Consider following sequence of events:
1. UFS is runtime suspended, link_state = Hibern8, device_state = sleep
2. System goes into system suspend, ufshcd_system_suspend() brings both
   link and device to active state and then puts the device in Power_Down
   state and link in OFF state.
3. System resumes at some later point in time, ufshcd_system_resume()
   doesn't do anything as UFS state is runtime suspended. Note that link
   is still on OFF state and device is in Power_Down state.
4. Now system again goes into suspend without any UFS accesses before it.
   ufshcd_system_suspend() again brings both link and device to active
   state and then puts the device in Power_Down state and link if OFF
   state. But it's unnecessary to bring the link & device in active state
   as both link and device are already in desired low power states. This
   change fixes this issue by adding proper state checks in
   ufshcd_system_suspend().

Reviewed-by: Gilad Broner <gbroner@codeaurora.org>
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>