Currently we have two routines that do practically the same thing
setup_IO_APIC_irq and io_apic_set_pci_routing.  This patch makes
setup_IO_APIC_irq the common factor of these two previous routines.
For setup_IO_APIC_irq all that was needed was to pass the trigger
and polarity to make the code a proper subset of io_apic_set_pci_routing.

Hopefully consolidating these two routines will improve maintenance
there were several differences that simply appear to be one routine
or the other getting it wrong.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>