ARM: dts: vf: Fix memory node duplication

Boards based on vf500/vf600 have duplicate memory nodes:

- One coming from the board dts file: memory@

- One coming from the vf500.dtsi/vf610m4.dtsi files.

Fix the duplication by removing the memory node from the dtsi file
and by adding 'device_type = "memory";' in the board dts.

Reported-by: Rob Herring <robh@kernel.org>
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
diff --git a/arch/arm/boot/dts/vf610-twr.dts b/arch/arm/boot/dts/vf610-twr.dts
index 59fceea..dbb5ffc 100644
--- a/arch/arm/boot/dts/vf610-twr.dts
+++ b/arch/arm/boot/dts/vf610-twr.dts
@@ -14,6 +14,7 @@
 	};
 
 	memory@80000000 {
+		device_type = "memory";
 		reg = <0x80000000 0x8000000>;
 	};