ARM: mvebu: add UART labels to Armada 375

This commit adds the standard uart0 and uart1 DT labels to the Device
Tree description of the Marvell Armada 375 SoC.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>

arch/arm/boot/dts/armada-375.dtsi

@@ -276,7 +276,7 @@ i2c1: i2c@11100 {
 				status = "disabled";
 			};
 
-			serial@12000 {
+			uart0: serial@12000 {
 				compatible = "snps,dw-apb-uart";
 				reg = <0x12000 0x100>;
 				reg-shift = <2>;
@@ -286,7 +286,7 @@ serial@12000 {
 				status = "disabled";
 			};
 
-			serial@12100 {
+			uart1: serial@12100 {
 				compatible = "snps,dw-apb-uart";
 				reg = <0x12100 0x100>;
 				reg-shift = <2>;