dt-bindings: serial: Document ma35d1 uart controller

Add documentation that describes the nuvoton ma35d1 UART driver bindings.
Signed-off-by: Jacky Huang <ychuang3@nuvoton.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Documentation/devicetree/bindings/serial/nuvoton,ma35d1-serial.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/serial/nuvoton,ma35d1-serial.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Nuvoton MA35D1 Universal Asynchronous Receiver/Transmitter (UART)
+
+maintainers:
+  - Min-Jen Chen <mjchen@nuvoton.com>
+  - Jacky Huang <ychuang3@nuvoton.com>
+
+allOf:
+  - $ref: serial.yaml
+
+properties:
+  compatible:
+    const: nuvoton,ma35d1-uart
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - clocks
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+    #include <dt-bindings/clock/nuvoton,ma35d1-clk.h>
+
+    serial@40700000 {
+        compatible = "nuvoton,ma35d1-uart";
+        reg = <0x40700000 0x100>;
+        interrupts = <GIC_SPI 59 IRQ_TYPE_LEVEL_HIGH>;
+        clocks = <&clk UART0_GATE>;
+    };
+...