arm64: dts: rockchip: Add support for Khadas Edge

Add devicetree support for Khadas Edge.
Khadas Edge is an expandable Rockchip RK3399 board with goldfinger.

Specification
- Rockchip RK3399
- Dual-Channel 2GB/4GB LPDDR4
- Onboard 16GB/32GB/128GB eMMC
- RTL8211FD 1Gbps
- AP6356S/AP6398S WiFI/BT
- HDMI Out, DP
- USB 3.0, 2.0
- USB Type C power and data
- 16MB SPI Flash
- Programmable MCU

Commit details of rk3399-khadas-edge-*.dts sync from Linux 5.3-rc2:
"arm64: dts: rockchip: Add support for Khadas Edge/Edge-V/Captain boards"
(sha1: c2aacceedc86af87428d998e23a1aca24fd8aa2e)

Signed-off-by: Nick Xie <nick@khadas.com>
Tested-by: Chris Webb <chris@arachsys.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>