scsi: ufs: ufs-mediatek: Support low-power mode for parents of VCCQx

Provide the facility to configure parents of VCCQx power rails as low-power
or full-power mode in MediaTek UFS platforms.

Link: https://lore.kernel.org/r/20220616053725.5681-9-stanley.chu@mediatek.com
Signed-off-by: Alice Chao <alice.chao@mediatek.com>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>