PCI: portdrv: cleanup pcie_device registration

In the current port bus driver implementation, pcie_device allocation,
initialization and registration are done in separated functions. Doing
those in one function make the code simple and easier to read.

Signed-off-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>