m68knommu: external interrupt support to ColdFire intc-2 controller

The EDGE Port module of some ColdFire parts using the intc-2 interrupt
controller provides support for 7 external interrupts. These interrupts
go off-chip (that is they are not for internal peripherals). They need
some special handling and have some extra setup registers. Add code to
support them.

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