ARM: dts: alpine: align UART node name with bindings

Bindings expect UART/serial node names to be "serial".

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Krzysztof Kozlowski <[e-mail]>

arch/arm/boot/dts/alpine.dtsi

···
 				     <GIC_SPI 71 IRQ_TYPE_LEVEL_HIGH>;
 		};
 
-		uart0: uart@fd883000 {
+		uart0: serial@fd883000 {
 			compatible = "ns16550a";
 			reg = <0x0 0xfd883000 0x0 0x1000>;
 			clock-frequency = <375000000>;
···
 			reg-io-width = <4>;
 		};
 
-		uart1: uart@fd884000 {
+		uart1: serial@fd884000 {
 			compatible = "ns16550a";
 			reg = <0x0 0xfd884000 0x0 0x1000>;
 			clock-frequency = <375000000>;