rockchip: rk3399: Add ROC-RK3399-PC support

Add initial support for ROC-RK3399-PC board.

Specification
- Rockchip RK3399
- LPDDR4 4GiB
- eMMC slot
- SD card slot
- RTL8211E 1Gbps
- HDMI Out, DP, MIPI DSI/CSI, EDP
- PCIe M.2
- USB 2.0, USB-3.0
- USB C Type

Commit details of rk3399-roc-pc.dts sync from Linux v5.2:
"arm64: dts: rockchip: add support for ROC-RK3399-PC board"
(sha1: 8bb878cf20ae10809c36db96993bfce7026d062b)

Signed-off-by: Levin Du <djw@t-chip.com.cn>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/board/rockchip/evb_rk3399/MAINTAINERS b/board/rockchip/evb_rk3399/MAINTAINERS
index d9711ab..f8299d9 100644
--- a/board/rockchip/evb_rk3399/MAINTAINERS
+++ b/board/rockchip/evb_rk3399/MAINTAINERS
@@ -49,6 +49,12 @@
 F:	arch/arm/dts/rk3399-u-boot.dtsi
 F:	arch/arm/dts/rk3399-orangepi-u-boot.dtsi
 
+ROC-RK3399-PC
+M:	Levin Du <djw@t-chip.com.cn>
+S:	Maintained
+F:	configs/roc-rk3399-pc_defconfig
+F:	arch/arm/dts/rk3399-roc-pc-u-boot.dtsi
+
 ROCK-PI-4
 M:	Akash Gajjar <akash@openedev.com>
 M:	Jagan Teki <jagan@amarulasolutions.com>