dt-bindings: mmc: Add support for BCM2712 SD host controller

dt-bindings: mmc: Add support for BCM2712 SD host controller

The BCM2712 has an SDHCI capable host interface similar to the one found
in other STB chipsets. Add the relevant compatible string.

Signed-off-by: Andrea della Porta <andrea.porta@suse.com>
Reviewed-by: Stefan Wahren <wahrenst@gmx.net>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/f6e0d1fbc6c5e620897b5c65c95147ceaeed1485.1717061147.git.andrea.porta@suse.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>