rockchip: rk3399: Add Nanopi NEO4 board support

rockchip: rk3399: Add Nanopi NEO4 board support

Add initial support for Nanopi NEO4 board.

Specification
- Rockchip RK3399
- 1GB DDR3-1866
- SD card slot
- eMMC Socket
- RTL8211E 1Gbps
- AP6212 WiFI/BT
- HDMI In/Out, DP, MIPI CSI
- USB 3.0, 2.0
- USB Type C power and data
- GPIO expansion ports
- DC 5V/3A

Commit details of rk3399-nanopi-neo4.dts sync from Linux:
"arm64: dts: rockchip: Add Nanopi NEO4 initial support"
(sha1: 092470b537f19788d957aed12d835a179b606014)

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