PCI: portdrv: cleanup service irqs initialization

This patch cleans up the service irqs initialization as follows:

 - Remove 'irq_mode' field in pcie_port_data and related definitions,
   which is not needed because we can get the same information from
   'is_msix', 'is_msi' and 'pin' fields in struct pci_dev.

 - Change the name of 'vectors' argument of assign_interrupt_mode() to
   'irqs' because it holds irq numbers actually. People might confuse
   it with CPU vector or MSI/MSI-X vector.

 - Change function name assign_interrupt_mode() to init_service_irqs()
   becasuse we no longer have 'irq_mode' data structure, and new name
   is more straightforward (IMO).

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