arm64: dts: mt7622: add mt7531 dsa to mt7622-rfb1 board

Add mt7531 dsa to mt7622-rfb1 board for 5 giga Ethernet ports support.
mt7622 only supports 1 sgmii interface, so either gmac0 or gmac1 can be
configured as sgmii interface. In this patch, change to connect mt7622
gmac0 and mt7531 port6 through sgmii interface.
Signed-off-by: Landen Chao <landen.chao@mediatek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/arm64/boot/dts/mediatek/mt7622-rfb1.dts

@@ -105,20 +105,71 @@ &eth {
 	pinctrl-0 = <&eth_pins>;
 	status = "okay";
 
-	gmac1: mac@1 {
+	gmac0: mac@0 {
 		compatible = "mediatek,eth-mac";
-		reg = <1>;
-		phy-handle = <&phy5>;
+		reg = <0>;
+		phy-mode = "2500base-x";
+
+		fixed-link {
+			speed = <2500>;
+			full-duplex;
+			pause;
+		};
 	};
 
 	mdio-bus {
 		#address-cells = <1>;
 		#size-cells = <0>;
 
-		phy5: ethernet-phy@5 {
-			reg = <5>;
-			phy-mode = "sgmii";
+		switch@0 {
+			compatible = "mediatek,mt7531";
+			reg = <0>;
+			reset-gpios = <&pio 54 0>;
+
+			ports {
+				#address-cells = <1>;
+				#size-cells = <0>;
+
+				port@0 {
+					reg = <0>;
+					label = "lan0";
+				};
+
+				port@1 {
+					reg = <1>;
+					label = "lan1";
+				};
+
+				port@2 {
+					reg = <2>;
+					label = "lan2";
+				};
+
+				port@3 {
+					reg = <3>;
+					label = "lan3";
+				};
+
+				port@4 {
+					reg = <4>;
+					label = "wan";
+				};
+
+				port@6 {
+					reg = <6>;
+					label = "cpu";
+					ethernet = <&gmac0>;
+					phy-mode = "2500base-x";
+
+					fixed-link {
+						speed = <2500>;
+						full-duplex;
+						pause;
+					};
+				};
+			};
 		};
+
 	};
 };