PCI: Move pci_rescan_bus() back to probe.c

We have pci_assign_unassigned_bus_resources() in as global function now.

Move pci_rescan_bus() back to probe.c where it should be.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>