pci: Add Rockchip PCIe controller driver

Add Rockchip PCIe controller driver for rk3399 platform.

Driver support Gen1 by operating as a Root complex.

Thanks to Patrick for initial work.

Signed-off-by: Patrick Wildt <patrick@blueri.se>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Tested-by: Suniel Mahesh <sunil@amarulasolutions.com> #roc-rk3399-pc