rockchip: rk3399: Add Leez P710 support

Specification
- Rockchip RK3399
- 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

Commit details of rk3399-leez-p710.dts sync from linus tree for Linux 5.4-rc1:
"arm64: dts: rockchip: Add dts for Leez RK3399 P710 SBC"
(sha1: 	fc702ed49a8668a17343811ee28214d845bfc5e6)

Signed-off-by: Andy Yan <andyshrk@gmail.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>

board/rockchip/evb_rk3399/MAINTAINERS

@@ -24,6 +24,12 @@ S:	Maintained
 F:	configs/khadas-edge-v-rk3399_defconfig
 F:	arch/arm/dts/rk3399-khadas-edge-v-u-boot.dtsi
 
+LEEZ-P710
+M:	Andy Yan <andy.yan@rock-chips.com>
+S:      Maintained
+F:	arch/arm/dts/rk3399-leez-p710-u-boot.dtsi
+F:	configs/leez-rk3399_defconfig
+
 NANOPC-T4
 M:	Jagan Teki <jagan@amarulasolutions.com>
 S:	Maintained