ARM: dts: imx6sx-udoo: Add board specific compatible strings

Add a compatible entry for the specific board versions.
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6sx-udoo-neo-basic.dts

@@ -46,7 +46,7 @@
 
 / {
 	model = "UDOO Neo Basic";
-	compatible = "fsl,imx6sx";
+	compatible = "udoo,neobasic", "fsl,imx6sx";
 
 	memory {
 		reg = <0x80000000 0x20000000>;

arch/arm/boot/dts/imx6sx-udoo-neo-extended.dts

@@ -46,7 +46,7 @@
 
 / {
 	model = "UDOO Neo Extended";
-	compatible = "fsl,imx6sx";
+	compatible = "udoo,neoextended", "fsl,imx6sx";
 
 	memory {
 		reg = <0x80000000 0x40000000>;

arch/arm/boot/dts/imx6sx-udoo-neo-full.dts

@@ -46,7 +46,7 @@
 
 / {
 	model = "UDOO Neo Full";
-	compatible = "fsl,imx6sx";
+	compatible = "udoo,neofull", "fsl,imx6sx";
 
 	memory {
 		reg = <0x80000000 0x40000000>;