dt-bindings: rtc: alphascale,asm9260-rtc: convert to dtschema

Convert existing binding to dtschema to support validation.

This is a direct conversion with no additions.
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20240326-rtc-yaml-v3-2-caa430ecace7@gmail.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Documentation/devicetree/bindings/rtc/alphascale,asm9260-rtc.txt

-* Alphascale asm9260 SoC Real Time Clock
-
-Required properties:
-- compatible: Should be "alphascale,asm9260-rtc"
-- reg: Physical base address of the controller and length
-       of memory mapped region.
-- interrupts: IRQ line for the RTC.
-- clocks: Reference to the clock entry.
-- clock-names: should contain:
-  * "ahb" for the SoC RTC clock
-
-Example:
-rtc0: rtc@800a0000 {
-	compatible = "alphascale,asm9260-rtc";
-	reg = <0x800a0000 0x100>;
-	clocks = <&acc CLKID_AHB_RTC>;
-	clock-names = "ahb";
-	interrupts = <2>;
-};

Documentation/devicetree/bindings/rtc/alphascale,asm9260-rtc.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/rtc/alphascale,asm9260-rtc.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Alphascale asm9260 SoC Real Time Clock
+
+maintainers:
+  - Javier Carrasco <javier.carrasco.cruz@gmail.com>
+
+allOf:
+  - $ref: rtc.yaml#
+
+properties:
+  compatible:
+    const: alphascale,asm9260-rtc
+
+  reg:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+  clock-names:
+    const: ahb
+
+  interrupts:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - clocks
+  - clock-names
+  - interrupts
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/clock/alphascale,asm9260.h>
+
+    rtc@800a0000 {
+        compatible = "alphascale,asm9260-rtc";
+        reg = <0x800a0000 0x100>;
+        clocks = <&acc CLKID_AHB_RTC>;
+        clock-names = "ahb";
+        interrupts = <2>;
+    };