dt-bindings: display: add data-mapping to panel-dpi

Add data-mapping property that can be used to specify
the media format used for the connection betwwen the
display controller (connector) and the panel.

v2:
  - drop lvds666 (Rob)

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200216181513.28109-5-sam@ravnborg.org

Documentation/devicetree/bindings/display/panel/panel-dpi.yaml

@@ -21,6 +21,15 @@ properties:
       - {}
       - const: panel-dpi
 
+  data-mapping:
+    enum:
+      - rgb24
+      - rgb565
+      - bgr666
+    description: |
+      Describes the media format, how the display panel is connected
+      to the display interface.
+
   backlight: true
   enable-gpios: true
   height-mm: true
@@ -43,7 +52,7 @@ examples:
         compatible = "osddisplays,osd057T0559-34ts", "panel-dpi";
         label = "osddisplay";
         power-supply = <&vcc_supply>;
-
+        data-mapping = "rgb565";
         backlight = <&backlight>;
 
         port {