dt-bindings: display: sun4i: New compatibles for A20 tcons

Document new compatibles used to differentiate between timing
controllers on A20 (sun7i)

Signed-off-by: Andrey Lebedev <andrey@lebedev.lt>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20200219180858.4806-5-andrey.lebedev@gmail.com

Documentation/devicetree/bindings/display/allwinner,sun4i-a10-tcon.yaml

@@ -34,6 +34,12 @@ properties:
       - const: allwinner,sun9i-a80-tcon-lcd
       - const: allwinner,sun9i-a80-tcon-tv
 
+      - items:
+        - enum:
+          - allwinner,sun7i-a20-tcon0
+          - allwinner,sun7i-a20-tcon1
+        - const: allwinner,sun7i-a20-tcon
+
       - items:
         - enum:
             - allwinner,sun50i-a64-tcon-lcd