dt-bindings: arm: realtek: Add ProBox2 AVA

Document a compatible string for the PROBOX2 AVA TV Box.

Cc: support@probox2.com
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NAndreas Färber <afaerber@suse.de>

Documentation/devicetree/bindings/arm/realtek.txt

@@ -12,6 +12,7 @@ Required root node properties:
 
 Root node property compatible must contain, depending on board:
 
+ - ProBox2 AVA: "probox2,ava"
  - Zidoo X9S: "zidoo,x9s"