regulator: dt-bindings: dlg,da9121: add buck2 constraints

Instead of describing the constraints for some devices (buck2 not
present), code it in allOf:if:then section to actually allow validation
of this requirement.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230725124629.150113-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/regulator/dlg,da9121.yaml

@@ -97,8 +97,6 @@ properties:
         properties:
           regulator-name:
             pattern: "^BUCK([1-2])$"
-            description: |
-              BUCK2 present in DA9122, DA9220, DA9131, DA9132 only
 
           regulator-initial-mode:
             enum: [ 0, 1, 2, 3 ]
@@ -122,6 +120,23 @@ required:
   - reg
   - regulators
 
+allOf:
+  - if:
+      properties:
+        compatible:
+          not:
+            contains:
+              enum:
+                - dlg,da9122
+                - dlg,da9131
+                - dlg,da9132
+                - dlg,da9220
+    then:
+      properties:
+        regulators:
+          properties:
+            buck2: false
+
 additionalProperties: false
 
 examples: