Have ampintcmsi(4) go through the list of interrupt controllers to find the

Have ampintcmsi(4) go through the list of interrupt controllers to find the
correct parent.  So far we were directly calling some ampintc(4) code, which
is fine for regular hardware.  With Parallels on the Apple M1, ampintcmsi(4)
is combined with agintc(4), which is quite a surprise.  Luckily both types of
interrupt controllers use the same API for passing interrupt information, so
we can craft one structure and both ampintc(4) and agintc(4) will happily work
with it.

ok kettenis@