mmc: renesas_sdhi_internal_dmac: Add R7S9210 support

The SDHI/MMC controller in the RZ/A2 is almost the same as R-Car gen3, but
with some minor differences.

Signed-off-by: Chris Brandt <chris.brandt@renesas.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>