ARM: mvebu: a38x: Add missing labels

The pintcrl label was missing. Adding it allowed referring it from the
root of the device tree. Also add the uart0 label used by the
bootloader.
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>

arch/arm/boot/dts/armada-38x.dtsi

@@ -173,7 +173,7 @@ i2c1: i2c@11100 {
 				status = "disabled";
 			};
 
-			serial@12000 {
+			uart0: serial@12000 {
 				compatible = "snps,dw-apb-uart";
 				reg = <0x12000 0x100>;
 				reg-shift = <2>;
@@ -193,7 +193,7 @@ serial@12100 {
 				status = "disabled";
 			};
 
-			pinctrl@18000 {
+			pinctrl: pinctrl@18000 {
 				reg = <0x18000 0x20>;
 
 				ge0_rgmii_pins: ge-rgmii-pins-0 {