scsi: ufs: allow configuring power mode without reading it

To enable configuring different power modes (number of lanes,
gear number and fast/slow modes) it is necessary to split the
configuration stage from the stage that reads the device max power mode.
In addition, it is not required to read the configuration more than
once, thus the configuration is stored after reading it once.

Change-Id: If79898eebda3c89d512fcbdf1e7d361de756dcc0
Signed-off-by: Dolev Raviv <draviv@codeaurora.org>