mmc: prepare tmio_mmc for passing of DMA configuration from the MFD cell

After this patch, if the "dma" pointer in struct tmio_mmc_data is not NULL, it
points to a struct, containing two tokens, that have to be passed to the
dmaengine driver for channel configuration.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>