intel-iommu: add ioapic irq test

IOAPIC irqs are line-based irqs comparing to MSI ones (which are
memory-based). To make it complete, let's also test IOAPIC interrupts
in the IR testcase.

Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>