ARM: ux500: Stop passing MMC's platform data for Device Tree boots

It was required to pass DMA channel configuration information to the
MMC driver before the new DMA API was in place. Now that it is, and
is fully compatible with Device Tree we can stop doing that.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>