scsi: ufs-mediatek: Add HS-G4 support

Provide HS-G4 support in MediaTek UFS platforms.

To support HS-G4, introduce mechanism to get the MediaTek UFS controller
version. With such information, driver can make right decision to apply
different configurations in different controllers.

Link: https://lore.kernel.org/r/20201029115750.24391-7-stanley.chu@mediatek.com


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