rockchip: rk3399: Add Nanopc T4 board support

rockchip: rk3399: Add Nanopc T4 board support

Add initial support for Nanopc T4 board.

Specification
- Rockchip RK3399
- Dual-Channel 4GB LPDDR3-1866
- SD card slot
- 16GB eMMC
- RTL8211E 1Gbps
- AP6356S WiFI/BT
- HDMI In/Out, DP, MIPI DSI/CSI, eDP
- USB 3.0, 2.0
- USB Type C power and data
- GPIO expansion ports
- DC 12V/2A

Commit details of rk3399-nanopc-t4.dts sync from Linux 5.1-rc2:
"arm64: dts: rockchip: Add NanoPC-T4 IR receiver"
(sha1: 95658e21b1707ad7844f873db2fdaa295109a5a3)

Tested-by: Daniel Gröber <dxld@darkboxed.org>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>