arm64: dts: imx8m: add SoC ID compatible

Add compatible string to .dtsi files for binding of imx8_soc_info and
device.
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Alice Guo <alice.guo@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mm.dtsi

@@ -257,7 +257,7 @@ usbphynop2: usbphynop2 {
 	};
 
 	soc@0 {
-		compatible = "simple-bus";
+		compatible = "fsl,imx8mm-soc", "simple-bus";
 		#address-cells = <1>;
 		#size-cells = <1>;
 		ranges = <0x0 0x0 0x0 0x3e000000>;

arch/arm64/boot/dts/freescale/imx8mn.dtsi

@@ -241,7 +241,7 @@ timer {
 	};
 
 	soc@0 {
-		compatible = "simple-bus";
+		compatible = "fsl,imx8mn-soc", "simple-bus";
 		#address-cells = <1>;
 		#size-cells = <1>;
 		ranges = <0x0 0x0 0x0 0x3e000000>;

arch/arm64/boot/dts/freescale/imx8mp.dtsi

@@ -218,7 +218,7 @@ timer {
 	};
 
 	soc@0 {
-		compatible = "simple-bus";
+		compatible = "fsl,imx8mp-soc", "simple-bus";
 		#address-cells = <1>;
 		#size-cells = <1>;
 		ranges = <0x0 0x0 0x0 0x3e000000>;

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

@@ -286,7 +286,7 @@ timer {
 	};
 
 	soc@0 {
-		compatible = "simple-bus";
+		compatible = "fsl,imx8mq-soc", "simple-bus";
 		#address-cells = <1>;
 		#size-cells = <1>;
 		ranges = <0x0 0x0 0x0 0x3e000000>;