arm64: dts: rockchip: Add support for Rock960 board

Add devicetree support for Rock960 board, one of the Consumer Edition
boards of the 96Boards family. This board support utilizes the common
Rock960 family board support that includes Ficus 96Board.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>