arm64: dts: rk3399-evb: Move u-boot properties into -u-boot.dtsi

Move U-Boot specific properties into rk3399-evb u-boot
specific dtsi file.

This would help to sync the devicetrees from Linux whenever
required instead of adding specific nodes.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>