PCI: Move pci_configure_slot() to drivers/pci/probe.c

Move pci_configure_slot() and related functions from
drivers/pci/hotplug/pcihp_slot to drivers/pci/probe.c.

This is to prepare for doing device configuration during the normal
enumeration process instead of just after hot-add.

No functional change.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>