dt-bindings: rtc: Add Mstar SSD202D RTC

Add YAML bindings for Mstar SSD202D RTC.
Signed-off-by: Romain Perier <romain.perier@gmail.com>
Link: https://lore.kernel.org/r/20230913151606.69494-3-romain.perier@gmail.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Documentation/devicetree/bindings/rtc/mstar,ssd202d-rtc.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/rtc/mstar,ssd202d-rtc.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Mstar SSD202D Real Time Clock
+
+maintainers:
+  - Daniel Palmer <daniel@0x0f.com>
+  - Romain Perier <romain.perier@gmail.com>
+
+allOf:
+  - $ref: rtc.yaml#
+
+properties:
+  compatible:
+    enum:
+      - mstar,ssd202d-rtc
+  reg:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    rtc@6800 {
+        compatible = "mstar,ssd202d-rtc";
+        reg = <0x6800 0x200>;
+    };
+...