ARM: dts: imx6sl: Fix memory node duplication

Boards based on imx6sl have duplicate memory nodes:

- One coming from the board dts file: memory@

- One coming from the imx6sl.dtsi file.

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 <[e-mail]>
Signed-off-by: Fabio Estevam <[e-mail]>
Signed-off-by: Shawn Guo <[e-mail]>

arch/arm/boot/dts/imx6sl-evk.dts

···
 	};
 
 	memory@80000000 {
+		device_type = "memory";
 		reg = <0x80000000 0x40000000>;
 	};
 

arch/arm/boot/dts/imx6sl-warp.dts

···
 	compatible = "warp,imx6sl-warp", "fsl,imx6sl";
 
 	memory@80000000 {
+		device_type = "memory";
 		reg = <0x80000000 0x20000000>;
 	};
 

arch/arm/boot/dts/imx6sl.dtsi

···
 	 * The decompressor and also some bootloaders rely on a
 	 * pre-existing /chosen node to be available to insert the
 	 * command line and merge other ATAGS info.
-	 * Also for U-Boot there must be a pre-existing /memory node.
 	 */
 	chosen {};
-	memory { device_type = "memory"; };
 
 	aliases {
 		ethernet0 = &fec;

arch/arm/boot/dts/imx6sll-evk.dts

···
 	};
 
 	memory@80000000 {
+		device_type = "memory";
 		reg = <0x80000000 0x80000000>;
 	};