dt-bindings: rtc: add bindings for microchip mpfs rtc

Add device tree bindings for the real time clock on
the Microchip PolarFire SoC.
Signed-off-by: Daire McNamara <daire.mcnamara@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Documentation/devicetree/bindings/rtc/microchip,mfps-rtc.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/rtc/microchip,mfps-rtc.yaml#
+
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Microchip PolarFire Soc (MPFS) RTC Device Tree Bindings
+
+allOf:
+  - $ref: rtc.yaml#
+
+maintainers:
+  - Daire McNamara <daire.mcnamara@microchip.com>
+  - Lewis Hanly <lewis.hanly@microchip.com>
+
+properties:
+  compatible:
+    enum:
+      - microchip,mpfs-rtc
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    items:
+      - description: |
+          RTC_WAKEUP interrupt
+      - description: |
+          RTC_MATCH, asserted when the content of the Alarm register is equal
+          to that of the RTC's count register.
+
+  clocks:
+    maxItems: 1
+
+  clock-names:
+    items:
+      - const: rtc
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - clocks
+  - clock-names
+
+additionalProperties: false
+
+examples:
+  - |
+    rtc@20124000 {
+        compatible = "microchip,mpfs-rtc";
+        reg = <0x20124000 0x1000>;
+        clocks = <&clkcfg 21>;
+        clock-names = "rtc";
+        interrupts = <80>, <81>;
+    };
+...