dt-bindings: media: nxp,imx-mipi-csi2: Add fsl,num-channels property

The CSI-2 receiver can be instantiated with up to four output channels.
This is an integration-specific property, specify the number of
instantiated channels through a new fsl,num-channels property. The
property is optional, and defaults to 1 as only one channel is currently
supported by drivers.

Using the compatible string to infer the number of channels has been
considered, but multiple instances of the same CSIS in the same SoC
could conceptually be synthesized with a different number of channels.
An explicit property is therefore more appropriate.

The only known SoC to have more than one channel is the i.MX8MP. As the
binding examples do not cover that SoC, don't update them.

Link: https://lore.kernel.org/r/20250822002734.23516-12-laurent.pinchart@ideasonboard.com
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>

Documentation/devicetree/bindings/media/nxp,imx-mipi-csi2.yaml

@@ -68,6 +68,13 @@ properties:
     default: 166000000
     deprecated: true
 
+  fsl,num-channels:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description: Number of output channels
+    minimum: 1
+    maximum: 4
+    default: 1
+
   ports:
     $ref: /schemas/graph.yaml#/properties/ports