arm64: dts: mediatek: x20: Add pinmux support for UART1

Add pinmux support for UART1 on MediatekX20 Development board based
on Mediatek MT6797 SoC.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>

arch/arm64/boot/dts/mediatek/mt6797-x20-dev.dts

@@ -30,4 +30,6 @@
 
 &uart1 {
 	status = "okay";
+	pinctrl-names = "default";
+	pinctrl-0 = <&uart1_pins_a>;
 };

arch/arm64/boot/dts/mediatek/mt6797.dtsi

@@ -141,6 +141,13 @@
 			    "iocfgr", "iocfgt";
 		gpio-controller;
 		#gpio-cells = <2>;
+
+		uart1_pins_a: uart1 {
+			pins1 {
+				pinmux = <MT6797_GPIO232__FUNC_URXD1>,
+					 <MT6797_GPIO233__FUNC_UTXD1>;
+			};
+		};
 	};
 
 	scpsys: scpsys@10006000 {