Enable auto suspend capability in MediaTek UFS driver.

Link: https://lore.kernel.org/r/1568649411-5127-4-git-send-email-stanley.chu@mediatek.comReviewed-by: Avri Altman <avri.altman@wdc.com>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>