PCI: rockchip: Modularize

Now that we've exported pci_remap_iospace() and added proper remove()
support, there's no reason this can't be a loadable module.

Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Shawn Lin <shawn.lin@rock-chips.com>