dt-bindings: mmc: rockchip-dw-mshc: Document Rockchip RV1126

Add a compatible string for Rockchip RV1126 SoC.

Signed-off-by: Jagan Teki <jagan@edgeble.ai>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220723204335.750095-12-jagan@edgeble.ai


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>