dt-bindings: arm: sunxi: add FriendlyARM NanoPi Duo2

Adds bindings for the newly added NanoPi Duo2 board.
Signed-off-by: Karl Palsson <karlp@tweak.net.au>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>

Documentation/devicetree/bindings/arm/sunxi.yaml

@@ -211,6 +211,11 @@ properties:
           - const: friendlyarm,nanopi-a64
           - const: allwinner,sun50i-a64
 
+      - description: FriendlyARM NanoPi Duo2
+        items:
+          - const: friendlyarm,nanopi-duo2
+          - const: allwinner,sun8i-h3
+
       - description: FriendlyARM NanoPi M1
         items:
           - const: friendlyarm,nanopi-m1