sh: prepare the SDHI MFD driver to pass DMA configuration to tmio_mmc.c

Pass DMA slave IDs from platform down to the tmio_mmc driver, to be used
for dmaengine 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>