Let mmci DT parser only handle the specific bindings related to mmci
and extend the DT support by converting to the common mmc DT parser.

While both DT and platform data exist, DT takes precedence. If there
are supplied DT data, the card detect and write protect GPIOS are
enforced to be provided through it.
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>