PCI/portdrv: Merge pcieport_if.h into portdrv.h

pcieport_if.h contained the interfaces to register port service driver,
e.g., pcie_port_service_register().  portdrv.h contained internal data
structures of the port driver.

I don't think it's worth keeping those files separate, since both headers
and their users are all inside the PCI core.

Merge pcieport_if.h directly in drivers/pci/pcie/portdrv.h and update the
users to include that instead.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>