ARM: dts: rockchip: add missing device_type = "memory" to boards

The memory node is supposed to contain a device_type property marking
it as memory. The currently included boards miss this property.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm/boot/dts/rk3066a-marsboard.dts

@@ -48,6 +48,7 @@
 	compatible = "haoyu,marsboard-rk3066", "rockchip,rk3066a";
 
 	memory {
+		device_type = "memory";
 		reg = <0x60000000 0x40000000>;
 	};