m68knommu: stop using __do_IRQ

The use of __do_IRQ is deprecated, so lets stop using it.
Generally the interrupts on the supported processors here are
level triggered, so this is strait forward to switch over to
using the standard handle_level_irq flow handler. (Although
some ColdFire parts support edge triggered GPIO line  interrupts
we have no support for them yet).

Signed-off-by: Greg Ungerer <gerg@uclinux.org>