dt-bindings: lcdif: Do not require power-domains for i.MX6ULL

i.MX6UL(L) uses "fsl,imx6sx-lcdif" as fallback compatible string,
but has only very lightweight DISPLAY power domain. Its DISPLAY
power domain is not supported by the binding / Linux kernel at
the moment. Since the current setup is working, let's remove the
power-domain from being required for that platform to fix the warning
printed by CHECK_DTBS=y.

Fixes: f62678a77d ("dt-bindings: mxsfb: Document i.MX8M/i.MX6SX/i.MX6SL power-domains property")
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Sebastian Reichel <sre@kernel.org>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Link: https://lore.kernel.org/r/20240224213240.1854709-7-sre@kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/display/fsl,lcdif.yaml

@@ -120,13 +120,19 @@ allOf:
           maxItems: 1
         clock-names:
           maxItems: 1
+  - if:
+      properties:
+        compatible:
+          const: fsl,imx6sx-lcdif
+    then:
+      required:
+        - power-domains
   - if:
       properties:
         compatible:
           contains:
             enum:
               - fsl,imx6sl-lcdif
-              - fsl,imx6sx-lcdif
               - fsl,imx8mm-lcdif
               - fsl,imx8mn-lcdif
               - fsl,imx8mp-lcdif