arm64: dts: imx8dxl: Pass fsl,imx8dxl-sc-wdt

Pass 'fsl,imx8dxl-sc-wdt' to fix the following schema warning:

system-controller: watchdog:compatible:0: 'fsl,imx8qxp-sc-wdt' was expected
	from schema $id: http://devicetree.org/schemas/firmware/fsl,scu.yaml#
system-controller: watchdog:compatible: ['fsl,imx-sc-wdt'] is too short
	from schema $id: http://devicetree.org/schemas/firmware/fsl,scu.yaml#Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8dxl.dtsi

@@ -166,7 +166,7 @@ sc_pwrkey: keys {
 		};
 
 		watchdog {
-			compatible = "fsl,imx-sc-wdt";
+			compatible = "fsl,imx8dxl-sc-wdt", "fsl,imx-sc-wdt";
 			timeout-sec = <60>;
 		};