_PIC is an optional method, so we shouldn't be aborting the rest of the

_PIC is an optional method, so we shouldn't be aborting the rest of the
MADT processing if it is missing. This, combined with an earlier diff
from kettenis@ to fix MADT interrupt polarity processing, should resolve
the issues reported with QEMU/KVM ACPI power button presses when using
OpenBSD guests.

ok kettenis@, pirofti@
tested by myself and kettenis for the past few weeks