dt-bindings: arm: sunxi: Add compatible for Tanix TX6 board

Add new Oranth Tanix TX6 board compatible string to the bindings
documentation.
Signed-off-by: NJernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>

Documentation/devicetree/bindings/arm/sunxi.yaml

@@ -677,6 +677,11 @@ properties:
           - const: sinlinx,sina33
           - const: allwinner,sun8i-a33
 
+      - description: Tanix TX6
+        items:
+          - const: oranth,tanix-tx6
+          - const: allwinner,sun50i-h6
+
       - description: TBS A711 Tablet
         items:
           - const: tbs-biometrics,a711