ARM: omap: remove mmc platform data dma_mask and initialization

DMAengine uses the DMA engine device structure when mapping/unmapping
memory for DMA, so the MMC devices do not need their DMA masks
initialized (this reflects hardware: the MMC device is not the device
doing DMA.)

Tested-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>