rockchip: Enable PCIe/M.2 on rk3399 board w/ M.2

Enable PCIe/M.2 support on
- NanoPC-T4
- ROC-RK3399-PC Mezzanine boards.

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