mmc: sh_mobile_sdhi: enable 32bit DMA access

Now, sh_mobile_sdhi can use 32bit DMA access in R-Cer Gen2.
Let's use it.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>