Add devicetree binding schema for the SD interface block implemented on
Socionext Uniphier SoCs.

This SD interface block is attached outside SDHC, and has some SD related
functions such as clock control, reset control, mode switch, and so on.
Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20221213082449.2721-15-hayashi.kunihiko@socionext.comSigned-off-by: Rob Herring <robh@kernel.org>