scsi: ufs: add support for hibernate operations

Host <-> Device UniPro link can be put into Hibernate when unused to save
power. This patch adds API support to enter or exit from the Hibernate.
These APIs could be called from the driver's system/runtime PM
callbacks.

Change-Id: I1e99c75ae4667ac39132b691115a71c8a569a58f
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>