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: NAsutosh Das <asutoshd@codeaurora.org>
Signed-off-by: NStanley Chu <stanley.chu@mediatek.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>