PCI: PCIe portdrv: Rearrange code so that related things are together

Rearrange code in drivers/pci/pcie/portdrv_bus.c and
drivers/pci/pcie/portdrv_core.c so that related functions and data
structures are closer together.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>