arm64: dts: rockchip: Add support for Khadas Edge/Edge-V/Captain boards

Add devicetree support for Khadas Edge/Edge-V/Captain boards.
Khadas Edge is an expandable Rockchip RK3399 board with goldfinger.
Khadas Captain is the carrier board for Khadas Edge.
Khadas Edge-V is a Khadas VIM form factor Rockchip RK3399 board.

Signed-off-by: Nick Xie <nick@khadas.com>
[edge-captain and edge-v contain different components that are supposed
 to get added in future patches, so should stay separate while looking
 somewhat similar right now]
Signed-off-by: Heiko Stuebner <heiko@sntech.de>