Revert "[POWERPC] Don't get PCI IRQ from OF for devices with no IRQ"

This reverts commit 41550c51

.

Quoth Ben Herrenschmidt:
 "Please revert this one for now.  It seems to break G5s :( Looks like
  PCI cells inside Apple IO ASICs don't have a PCI_INTERRUPT_LINE set.
  I need to figure out a better fix."

Signed-off-by: Linus Torvalds <torvalds@osdl.org>