PCI: export pcie_bus_configure_settings symbol

pcie_bus_configure_settings needs to be exported if the PCI hotplug
driver is being compiled as a module.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Jon Mason <mason@myri.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>