arm64: dts: imx8mq: Add mux controller to iomuxc_gpr

The only mux controls the MIPI DSI input selection.
Signed-off-by: Guido Günther <agx@sigxcpu.org>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mq.dtsi

@@ -440,8 +440,15 @@ iomuxc: iomuxc@30330000 {
 			};
 
 			iomuxc_gpr: syscon@30340000 {
-				compatible = "fsl,imx8mq-iomuxc-gpr", "fsl,imx6q-iomuxc-gpr", "syscon";
+				compatible = "fsl,imx8mq-iomuxc-gpr", "fsl,imx6q-iomuxc-gpr",
+					     "syscon", "simple-mfd";
 				reg = <0x30340000 0x10000>;
+
+				mux: mux-controller {
+					compatible = "mmio-mux";
+					#mux-control-cells = <1>;
+					mux-reg-masks = <0x34 0x00000004>; /* MIPI_MUX_SEL */
+				};
 			};
 
 			ocotp: ocotp-ctrl@30350000 {