dt-bindings: rtc: sun6i: Clean up repetition

- Use "enum" for compatibles instead of several "const" alternatives.
- Merge the H6 clock-output-names minItems/maxItems constraint into the
  identical block above.
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Maxime Ripard <maxime@cerno.tech>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220203021736.13434-2-samuel@sholland.org

Documentation/devicetree/bindings/rtc/allwinner,sun6i-a31-rtc.yaml

@@ -16,16 +16,17 @@ properties:
 
   compatible:
     oneOf:
-      - const: allwinner,sun6i-a31-rtc
-      - const: allwinner,sun8i-a23-rtc
-      - const: allwinner,sun8i-h3-rtc
-      - const: allwinner,sun8i-r40-rtc
-      - const: allwinner,sun8i-v3-rtc
-      - const: allwinner,sun50i-h5-rtc
+      - enum:
+          - allwinner,sun6i-a31-rtc
+          - allwinner,sun8i-a23-rtc
+          - allwinner,sun8i-h3-rtc
+          - allwinner,sun8i-r40-rtc
+          - allwinner,sun8i-v3-rtc
+          - allwinner,sun50i-h5-rtc
+          - allwinner,sun50i-h6-rtc
       - items:
           - const: allwinner,sun50i-a64-rtc
           - const: allwinner,sun8i-h3-rtc
-      - const: allwinner,sun50i-h6-rtc
 
   reg:
     maxItems: 1
@@ -85,18 +86,7 @@ allOf:
             enum:
               - allwinner,sun8i-h3-rtc
               - allwinner,sun50i-h5-rtc
-
-    then:
-      properties:
-        clock-output-names:
-          minItems: 3
-          maxItems: 3
-
-  - if:
-      properties:
-        compatible:
-          contains:
-            const: allwinner,sun50i-h6-rtc
+              - allwinner,sun50i-h6-rtc
 
     then:
       properties: