scsi: ufs: ufs-mediatek: add waiting time for reference clock

Some delays may be required either after gating or before ungating
reference clock for device according to vendor requirements.

Note that in UFS 3.0, the delay time after gating reference
clock can be defined by attribute bRefClkGatingWaitTime. Use the
formal value instead if it can be queried from device.

Link: https://lore.kernel.org/r/20200220134848.8807-2-stanley.chu@mediatek.com


Reviewed-by: Bean Huo <beanhuo@micron.com>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>