ARM: dts: imx6ul iomuxc syscon is compatible to imx6q

The imx6ul iomuxc syscon is compatible to imx6q,
so let's add compatible string 'fsl,imx6q-iomuxc-gpr'
for imx6ul iomuxc syscon node.
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6ul.dtsi

@@ -644,7 +644,8 @@ iomuxc: iomuxc@020e0000 {
 			};
 
 			gpr: iomuxc-gpr@020e4000 {
-				compatible = "fsl,imx6ul-iomuxc-gpr", "syscon";
+				compatible = "fsl,imx6ul-iomuxc-gpr",
+					     "fsl,imx6q-iomuxc-gpr", "syscon";
 				reg = <0x020e4000 0x4000>;
 			};