PCI: Build setup-irq.o on all arches

The functions included in setup-irq.o currently apply only to a selection
of architectures which share common IRQ assignment code.  However this code
needs to be generalised for all arches to allow deferred IRQ assignment.
So the first step is to build it on all architectures.

Signed-off-by: Matthew Minter <matt@masarand.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>