Revert "scsi: ufs: stub UFS shutdown handler"

This reverts commit aa484ff4b600 ("scsi: ufs: stub UFS shutdown
handler").
This is reverted so as to enable PON (Power-off Notification).
PON would notify the ufs device of the incoming power-down
so that the device can prepare for the same before
the power to the device is cut.

CRs-fixed: 941978
Change-Id: Idee8691d769218d7e732c9b7f936a2c40946b239
Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>