arm64: dts: rockchip: add dts file for RK3399 evaluation board

This patch add rk3399-evb.dts for RK3399 evaluation board.
Tested on RK3399 evb.

Signed-off-by: Jianqun Xu <jay.xu@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>