ARM: dts: am572x: Add missing unit name to memory nodes

This patch fixes the following DTC warnings:

"Node /memory has a reg or ranges property, but no unit name"
Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/boot/dts/am572x-idk.dts

@@ -18,7 +18,7 @@ / {
 	compatible = "ti,am5728-idk", "ti,am5728", "ti,dra742", "ti,dra74",
 		     "ti,dra7";
 
-	memory {
+	memory@0 {
 		device_type = "memory";
 		reg = <0x0 0x80000000 0x0 0x80000000>;
 	};

arch/arm/boot/dts/am57xx-beagle-x15.dts

@@ -23,7 +23,7 @@ aliases {
 		display0 = &hdmi0;
 	};
 
-	memory {
+	memory@0 {
 		device_type = "memory";
 		reg = <0x0 0x80000000 0x0 0x80000000>;
 	};

arch/arm/boot/dts/am57xx-cl-som-am57x.dts

@@ -19,7 +19,7 @@ / {
 	model = "CompuLab CL-SOM-AM57x";
 	compatible = "compulab,cl-som-am57x", "ti,am5728", "ti,dra742", "ti,dra74", "ti,dra7";
 
-	memory {
+	memory@0 {
 		device_type = "memory";
 		reg = <0x0 0x80000000 0x0 0x20000000>; /* 512 MB - minimal configuration */
 	};