dt-binding: display: Allow a single port node on rocktech, jh057n00900

The display has one port. Allow it in the binding.
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Guido Günther <agx@sigxcpu.org>
Signed-off-by: Ondrej Jirman <megous@megous.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200703114717.2140832-3-megous@megous.com

Documentation/devicetree/bindings/display/panel/rocktech,jh057n00900.yaml

@@ -24,6 +24,7 @@ properties:
         # Xingbangda XBD599 5.99" 720x1440 TFT LCD panel
       - xingbangda,xbd599
 
+  port: true
   reg:
     maxItems: 1
     description: DSI virtual channel