mmc: tmio: sdhi: Configure internal DMA bus width

The R-Car3 SDHI should set these two bits in DMA_MODE register according
to the specification, to indicate 64bit bus width. No other bus width
options are permitted and the default value is 0, which is incorrect.
Set the bits accordingly.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>