dt-bindings: iio: adc: Add imx6ul & imx6sx compatibles

Both are already using the vf610 compatible.

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220613123529.466528-1-alexander.stein@ew.tq-group.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/fsl,vf610-adc.yaml

@@ -14,7 +14,14 @@ description:
 
 properties:
   compatible:
-    const: fsl,vf610-adc
+    oneOf:
+      - items:
+          - enum:
+              - fsl,imx6sx-adc
+              - fsl,imx6ul-adc
+          - const: fsl,vf610-adc
+      - items:
+          - const: fsl,vf610-adc
 
   reg:
     maxItems: 1