PCI: alpha: use generic pci_swizzle_interrupt_pin()

Use the generic pci_swizzle_interrupt_pin() instead of arch-specific code.

Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>