scsi: ufs-msm: add vendor specific support for power change callback

Sometimes, the device shall report its maximum power and speed
capabilities, but we might not wish to configure it to use those
maximum capabilities.

In this change we implement the vendor specific callback that should
determines what parameters we should use in power change.
It takes into account the maximum capabilities of the device, and
also the pre-defined vendor preferences.
According to both set of parameters, it calculates the maximum power
and speed that are still acceptable by both: the vendor preferences
and the devices capabilities.

Change-Id: I3ef468d3882f3ed9d49a99aa285af4a1f58063a0
Signed-off-by: Yaniv Gardi <ygardi@codeaurora.org>