dt-bindings: rtc: Add Nuvoton ma35d1 rtc

Add documentation describing the Nuvoton ma35d1 rtc controller.
Signed-off-by: Jacky Huang <ychuang3@nuvoton.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230925070251.28-2-ychuang570808@gmail.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

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

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/rtc/nuvoton,ma35d1-rtc.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Nuvoton MA35D1 Real Time Clock
+
+maintainers:
+  - Min-Jen Chen <mjchen@nuvoton.com>
+
+allOf:
+  - $ref: rtc.yaml#
+
+properties:
+  compatible:
+    enum:
+      - nuvoton,ma35d1-rtc
+
+  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>
+    rtc@40410000 {
+        compatible = "nuvoton,ma35d1-rtc";
+        reg = <0x40410000 0x200>;
+        interrupts = <GIC_SPI 5 IRQ_TYPE_EDGE_RISING>;
+        clocks = <&clk RTC_GATE>;
+    };
+
+...