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>