register_platform_device_full() can setup the DMA mask provided the
appropriate member is set in struct platform_device_info.  So lets
make that be the case.  This avoids a direct reference to the DMA
masks by this driver.

While here, add the dma_set_mask_and_coherent() call which the DMA API
requires DMA-using drivers to call.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>