scsi: ufs-qcom: enable/disable the device ref clock

This change enables the device ref clock before changing to HS mode
and disables it if entered to PWM mode.

Reviewed-by: Gilad Broner <gbroner@codeaurora.org>
Signed-off-by: Yaniv Gardi <ygardi@codeaurora.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>