scsi: ufs-mediatek: Decouple features from platform bindings

UFS proprietary features (including features introduced later) in MediaTek
UFS platforms have complicated combinations among different platforms.

To ease code readability and maintenance, decouple all proprietary features
from platform bindings. Each feature would be enabled only if specific
property string is defined in device tree node.

Link: https://lore.kernel.org/r/20201029115750.24391-4-stanley.chu@mediatek.com


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