Do IRQ determination generically by parsing the PROM properties,
and using IRQ controller drivers for final resolution.

One immediate positive effect is that all of the IRQ frobbing
in the EBUS, ISA, and PCI controller layers has been eliminated.
We just look up the of_device and use the properly computed
value.

The PCI controller irq_build() routines are gone and no longer
used.  Unfortunately sbus_build_irq() has to remain as there is
a direct reference to this in the sunzilog driver.  That can be
killed off once the sparc32 side of this is written and the
sunzilog driver is transformed into an "of" bus driver.

Signed-off-by: David S. Miller <davem@davemloft.net>