dt-bindings: nt35510: document 'port' property

Allow 'port' property (coming from panel-common.yaml) to be used in DTS:

  st/stm32f769-disco-mb1166-reva09.dtb: panel@0: 'port' does not match any of the regexes: 'pinctrl-[0-9]+'
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>

Documentation/devicetree/bindings/display/panel/novatek,nt35510.yaml

@@ -29,6 +29,7 @@ properties:
   vddi-supply:
     description: regulator that supplies the vddi voltage
   backlight: true
+  port: true
 
 required:
   - compatible