dt-bindings: mmc: mediatek: Add document for mt6779

Add compatible node for mt6779 mmc.
Signed-off-by: Chun-Hung Wu <chun-hung.wu@mediatek.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1595205759-5825-5-git-send-email-chun-hung.wu@mediatek.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/mtk-sd.txt

@@ -12,6 +12,7 @@ Required properties:
 	"mediatek,mt8173-mmc": for mmc host ip compatible with mt8173
 	"mediatek,mt8183-mmc": for mmc host ip compatible with mt8183
 	"mediatek,mt8516-mmc": for mmc host ip compatible with mt8516
+	"mediatek,mt6779-mmc": for mmc host ip compatible with mt6779
 	"mediatek,mt2701-mmc": for mmc host ip compatible with mt2701
 	"mediatek,mt2712-mmc": for mmc host ip compatible with mt2712
 	"mediatek,mt7622-mmc": for MT7622 SoC