PCI: PCIe portdrv: Add kerneldoc comments to remining core funtions

Add kerneldoc comments to the reamining functions in
drivers/pci/pcie/portdrv_core.c .

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