lantiq: dts: move memory node to board dts

The memory node is highly board specific and should be only defined in
the board dts.

Signed-off-by: Mathias Kresin <dev@kresin.me>

target/linux/lantiq/files/arch/mips/boot/dts/DGN1000B.dts

@@ -23,6 +23,7 @@
 	};
 
 	memory@0 {
+		device_type = "memory";
 		reg = <0x0 0x1000000>;
 	};