dt-bindings: mmc: renesas,sdhi: Document RZ/G3E support

dt-bindings: mmc: renesas,sdhi: Document RZ/G3E support

The SD/MMC block on the RZ/G3E ("R9A09G047") SoC is similar to that
of the RZ/V2H, but the SD0 channel has only dedicated pins, so we must
use SD_STATUS register to control voltage and power enable (internal
regulator), for non-fixed voltage (SD) MMC interface. However, it is
optional for fixed voltage MMC interface (eMMC).

For SD1 and SD2 channels, we can either use gpio regulator or internal
regulator (using SD_STATUS register) for voltage switching.

Document RZ/G3E SDHI IP support with optional internal regulator for
both RZ/G3E and RZ/V2H SoC.

Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://lore.kernel.org/r/20250305092958.21865-2-biju.das.jz@bp.renesas.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>