mmc: mxcmmc: Convert to devm-* API

Replace existing resource handling in the driver with managed
device resource, this ensures more consistent error values and
simplifies error paths.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Chris Ball <chris@printf.net>