PCI/PM: Drop unused runtime PM support code for PCIe ports

Since commit de7d5f72

 ("PCI/PM: Disable runtime PM of PCIe ports") the
runtime PM support code for PCIe ports in portdrv_pci.c has never been
used, so drop it entirely.

If we are to support runtime PM of PCIe ports, it will have to be done in a
different way most likely anyway.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>