mmc: sh_mmcif: make DMA support by the driver unconditional

Simplify the driver by removing the possibility to build it without the DMA
support and remove the respective Kconfig parameter.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>