BACKPORT: scsi: ufs-mediatek: Support VA09 regulator operations

Some MediaTek UFS platforms need to control VA09 power
specifically. Provide such control according to the device tree binding.

Bug: 188004633
Change-Id: I73b21edc92a52fa17c79415e6b77e3a5a4c35932
(cherry picked from commit cf137b3e)
[Stanley: Resolved minor conflict in drivers/scsi/ufs/ufs-mediatek.h]
Link: https://lore.kernel.org/r/20201029115750.24391-3-stanley.chu@mediatek.com


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