dt-bindings: adc: ad9467: add new io-backend property

The ad9467 will make use of the new IIO backend framework which is a
provider - consumer interface where IIO backends provide services to
consumers. As such, and being this device a consumer,  add the new
generic io-backend property to the bindings.
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20240210-iio-backend-v11-1-f5242a5fb42a@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/adi,ad9467.yaml

@@ -44,6 +44,9 @@ properties:
       Pin that controls the powerdown mode of the device.
     maxItems: 1
 
+  io-backends:
+    maxItems: 1
+
   reset-gpios:
     description:
       Reset pin for the device.
@@ -68,6 +71,7 @@ examples:
             reg = <0>;
             clocks = <&adc_clk>;
             clock-names = "adc-clk";
+            io-backends = <&iio_backend>;
         };
     };
 ...