dt-bindings: mmc: Add support for Mediatek MT7986

This commit adds dt-binding documentation of mmc for Mediatek MT7986 SoC
Platform.
Add SoC specific section for defining clock configuration.
Signed-off-by: Sam Shih <sam.shih@mediatek.com>
Signed-off-by: Frank Wunderlich <frank-w@public-files.de>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20221025132953.81286-3-linux@fw-web.deSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

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

@@ -20,6 +20,7 @@ properties:
           - mediatek,mt6795-mmc
           - mediatek,mt7620-mmc
           - mediatek,mt7622-mmc
+          - mediatek,mt7986-mmc
           - mediatek,mt8135-mmc
           - mediatek,mt8173-mmc
           - mediatek,mt8183-mmc
@@ -237,6 +238,31 @@ allOf:
         reg:
           minItems: 2
 
+  - if:
+      properties:
+        compatible:
+          contains:
+            enum:
+              - mediatek,mt7986-mmc
+    then:
+      properties:
+        clocks:
+          minItems: 3
+          items:
+            - description: source clock
+            - description: HCLK which used for host
+            - description: independent source clock gate
+            - description: bus clock used for internal register access (required for MSDC0/3).
+            - description: msdc subsys clock gate
+        clock-names:
+          minItems: 3
+          items:
+            - const: source
+            - const: hclk
+            - const: source_cg
+            - const: bus_clk
+            - const: sys_cg
+
   - if:
       properties:
         compatible: