[SCSI] ufs: wrap the i/o access operations

Simplify operations with hiding mmio_base.

Signed-off-by: Seungwon Jeon <tgih.jun@samsung.com>
Tested-by: Maya Erez <merez@codeaurora.org>
Signed-off-by: Santosh Y <santoshsy@gmail.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>