dt-bindings: rtc: Add Cirrus EP93xx

Add device tree bindings for the Cirrus Logic EP93xx RTC block
used in these SoCs.
Signed-off-by: Nikita Shubin <nikita.shubin@maquefel.me>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230915-ep93xx-v4-13-a1d779dcec10@maquefel.meSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Documentation/devicetree/bindings/rtc/cirrus,ep9301-rtc.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/rtc/cirrus,ep9301-rtc.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Cirrus EP93xx Real Time Clock controller
+
+maintainers:
+  - Hartley Sweeten <hsweeten@visionengravers.com>
+  - Alexander Sverdlin <alexander.sverdlin@gmail.com>
+
+allOf:
+  - $ref: rtc.yaml#
+
+properties:
+  compatible:
+    oneOf:
+      - const: cirrus,ep9301-rtc
+      - items:
+          - enum:
+              - cirrus,ep9302-rtc
+              - cirrus,ep9307-rtc
+              - cirrus,ep9312-rtc
+              - cirrus,ep9315-rtc
+          - const: cirrus,ep9301-rtc
+
+  reg:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    rtc@80920000 {
+        compatible = "cirrus,ep9301-rtc";
+        reg = <0x80920000 0x100>;
+    };