ARM: dts: imx7s: add multiplexer controls

The IOMUXC General Purpose Register has bitfield to control video bus
multiplexer to control the CSI input between the MIPI-CSI2 and parallel
interface. Add that register and mask.
Signed-off-by: NRui Miguel Silva <rui.silva@linaro.org>
Reviewed-by: NPhilipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: NShawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx7s.dtsi

@@ -497,8 +497,15 @@
 
 			gpr: iomuxc-gpr@30340000 {
 				compatible = "fsl,imx7d-iomuxc-gpr",
-					"fsl,imx6q-iomuxc-gpr", "syscon";
+					"fsl,imx6q-iomuxc-gpr", "syscon",
+					"simple-mfd";
 				reg = <0x30340000 0x10000>;
+
+				mux: mux-controller {
+					compatible = "mmio-mux";
+					#mux-control-cells = <0>;
+					mux-reg-masks = <0x14 0x00000010>;
+				};
 			};
 
 			ocotp: ocotp-ctrl@30350000 {