arm64: dts: rockchip: Add dts for Leez RK3399 P710 SBC

P710 is a RK3399 based SBC, designed by Leez [0].

Specification
- Rockchip RK3399
- 4/2GB LPDDR4
- TF sd scard slot
- eMMC
- M.2 B-Key for 4G LTE
- AP6256 for WiFi + BT
- Gigabit ethernet
- HDMI out
- 40 pin header
- USB 2.0 x 2
- USB 3.0 x 1
- USB 3.0 Type-C x 1
- TYPE-C Power supply

[0]https://leez.lenovo.com



Signed-off-by: Andy Yan <andyshrk@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>