The UFS driver is growing more and more customizable parameters. Collect
them in one place.

Link: https://lore.kernel.org/r/20200509093716.21010-2-stanley.chu@mediatek.comReviewed-by: Asutosh Das <asutoshd@codeaurora.org>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>