PCI: Export pci_remap_iospace() and pci_unmap_iospace()

These are useful for PCIe host drivers, and those drivers can be modules.

[bhelgaas: don't remove __weak; it's removed elsewhere]
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>