ARM: dts: ls1021a: Add label to USB controllers

Add usb2 and usb3 labels to USB2 and USB3 controller device tree nodes,
for easier modification in board dts files.
Signed-off-by: Esben Haabendal <eha@deif.com>
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/ls1021a.dtsi

@@ -689,7 +689,7 @@ queue-group@2d94000  {
 			};
 		};
 
-		usb@8600000 {
+		usb2: usb@8600000 {
 			compatible = "fsl-usb2-dr-v2.5", "fsl-usb2-dr";
 			reg = <0x0 0x8600000 0x0 0x1000>;
 			interrupts = <GIC_SPI 171 IRQ_TYPE_LEVEL_HIGH>;
@@ -697,7 +697,7 @@ usb@8600000 {
 			phy_type = "ulpi";
 		};
 
-		usb3@3100000 {
+		usb3: usb3@3100000 {
 			compatible = "snps,dwc3";
 			reg = <0x0 0x3100000 0x0 0x10000>;
 			interrupts = <GIC_SPI 93 IRQ_TYPE_LEVEL_HIGH>;