scsi: ufs: ufs-mediatek: Support low-power mode for VCCQ

Allow VCCQ to enter low-power mode, and also remove the restriction of VCC
because VCCQ/VCCQ2 can be changed to low-power mode even if VCC stays on
while the device is not in active power mode.

Link: https://lore.kernel.org/r/20220616053725.5681-7-stanley.chu@mediatek.com
Reviewed-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Peter Wang <peter.wang@mediatek.com>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>