mmc: renesas_sdhi_internal_dmac: add R8A77970 to whitelist

I've successfully tested eMMC on the V3H Starter Kit board and since the
R8A77970 SoC has a single SDHI core, it can't be a subject to the known RX
DMA errata.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>