dt-bindings: serial: 8250: Add Loongson uart compatible

The Loongson family have a mostly NS16550A-compatible UART and
High-Speed UART hardware with the exception of custom frequency divider
latch settings register.

Co-developed-by: Haowei Zheng <zhenghaowei@loongson.cn>
Signed-off-by: Haowei Zheng <zhenghaowei@loongson.cn>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Link: https://patch.msgid.link/2d858e9303d95a3e4909aa9c1379d4abbdc52cc2.1760166651.git.zhoubinbin@loongson.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: AaronDot

Documentation/devicetree/bindings/serial/8250.yaml

@@ -125,6 +125,8 @@ properties:
               - nxp,lpc1850-uart
               - opencores,uart16550-rtlsvn105
               - ti,da830-uart
+              - loongson,ls2k0500-uart
+              - loongson,ls2k1500-uart
           - const: ns16550a
       - items:
           - enum:
@@ -169,6 +171,18 @@ properties:
               - nvidia,tegra194-uart
               - nvidia,tegra234-uart
           - const: nvidia,tegra20-uart
+      - items:
+          - enum:
+              - loongson,ls2k1000-uart
+          - const: loongson,ls2k0500-uart
+          - const: ns16550a
+      - items:
+          - enum:
+              - loongson,ls3a5000-uart
+              - loongson,ls3a6000-uart
+              - loongson,ls2k2000-uart
+          - const: loongson,ls2k1500-uart
+          - const: ns16550a
 
   reg:
     maxItems: 1