scsi: ufs: Support query the spm/rpm level from device tree

Add support to query the system suspend and runtime suspend
pm levels from the device tree. Note if the pm level is set to
power down, the device's vcc will be turned
off during system suspend, and the host will do full device
power up sequence during system resume. This may have some impact
on the system resume latency and UFS device life time.

Change-Id: I9f1aaeb14e7947f0a5e474ebb3ea5981e5e502a7
Signed-off-by: Bao D. Nguyen <nguyenb@codeaurora.org>