rockchip: rk3568-radxa-e25: Enable pcie3x1 node

Enable mini PCIe slot, pcie3x1 node, now that the PCIe PHY driver
support bifurcation.

A pinctrl is assigned for reset-gpios or the device may freeze running
pci enum and nothing is connected to the mini PCIe slot.

Also drop the AHCI_PCI Kconfig option as this option is not required for
a functional M.2 SATA drive slot.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>