dt-bindings: mmc: renesas,sdhi: Document RZ/G3S support

Document support for the SD Card/MMC interface on the Renesas
RZ/G3S (R9A08G045) SoC.

Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230912045157.177966-32-claudiu.beznea.uj@bp.renesas.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>