dt-bindings: ili9881c: Allow port subnode

The ILI9881C is a DSI panel, which can be tied to a DSI controller
using OF graph port/endpoint. Allow the port subnode in the binding.

Signed-off-by: Marek Vasut <[e-mail]>
Reviewed-by: Neil Armstrong <[e-mail]>
Acked-by: Conor Dooley <[e-mail]>
Signed-off-by: Neil Armstrong <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Documentation/devicetree/bindings/display/panel/ilitek,ili9881c.yaml

···
     maxItems: 1
 
   backlight: true
+  port: true
   power-supply: true
   reset-gpios: true
   rotation: true