Documentation: devicetree: rockchip: Document rk3368-GeekBox

Use "geekbuying,geekbox" compatible string.
Signed-off-by: Andreas Färber <afaerber@suse.de>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

Documentation/devicetree/bindings/arm/rockchip.txt

@@ -39,6 +39,10 @@ Rockchip platforms device tree bindings
     Required root node properties:
       - compatible = "netxeon,r89", "rockchip,rk3288";
 
+- GeekBuying GeekBox:
+    Required root node properties:
+      - compatible = "geekbuying,geekbox", "rockchip,rk3368";
+
 - Google Brain (dev-board):
     Required root node properties:
       - compatible = "google,veyron-brain-rev0", "google,veyron-brain",