dt-bindings: add rockchip RK1108 Evaluation board

RK1108 EVB is designed by Rockchip for CVR field.
Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Acked-by: Rob Herring <robh@kernel.org>
[split off from dts patch and to prevent conflicts with px5 addition]
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

Documentation/devicetree/bindings/arm/rockchip.txt

@@ -107,6 +107,10 @@ Rockchip platforms device tree bindings
     Required root node properties:
       - compatible = "rockchip,px5-evb", "rockchip,px5", "rockchip,rk3368";
 
+- Rockchip RK1108 Evaluation board
+    Required root node properties:
+      - compatible = "rockchip,rk1108-evb", "rockchip,rk1108";
+
 - Rockchip RK3368 evb:
     Required root node properties:
       - compatible = "rockchip,rk3368-evb-act8846", "rockchip,rk3368";