scsi: ufs: add support for pre-defined device power preferences

Sometimes, the device shall report its maximum power and speed
capabilities, but we might not wish to configure it to use those
maximum capabilities.
This change adds support for the vendor specific host driver to
implement power change notify callback.

Change-Id: I5685d52bcad5941dac604bf72a9d21380f33aca3
Signed-off-by: Yaniv Gardi <ygardi@codeaurora.org>