LoongArch: dts: Add uart new compatible string

Add loongson,ls2k*-uart compatible string on uarts.

Co-developed-by: Haowei Zheng <zhenghaowei@loongson.cn>
Signed-off-by: Haowei Zheng <zhenghaowei@loongson.cn>
Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Link: https://patch.msgid.link/8e0c08459fa5bddefd898648fea28a9f2fde701a.1760166651.git.zhoubinbin@loongson.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: AaronDot

arch/loongarch/boot/dts/loongson-2k0500.dtsi

@@ -380,7 +380,7 @@
 		};
 
 		uart0: serial@1ff40800 {
-			compatible = "ns16550a";
+			compatible = "loongson,ls2k0500-uart", "ns16550a";
 			reg = <0x0 0x1ff40800 0x0 0x10>;
 			clock-frequency = <100000000>;
 			interrupt-parent = <&eiointc>;

arch/loongarch/boot/dts/loongson-2k1000.dtsi

@@ -297,7 +297,7 @@
 		};
 
 		uart0: serial@1fe20000 {
-			compatible = "ns16550a";
+			compatible = "loongson,ls2k1000-uart", "loongson,ls2k0500-uart", "ns16550a";
 			reg = <0x0 0x1fe20000 0x0 0x10>;
 			clock-frequency = <125000000>;
 			interrupt-parent = <&liointc0>;

arch/loongarch/boot/dts/loongson-2k2000.dtsi

@@ -250,7 +250,7 @@
 		};
 
 		uart0: serial@1fe001e0 {
-			compatible = "ns16550a";
+			compatible = "loongson,ls2k2000-uart", "loongson,ls2k1500-uart", "ns16550a";
 			reg = <0x0 0x1fe001e0 0x0 0x10>;
 			clock-frequency = <100000000>;
 			interrupt-parent = <&liointc>;