Currently, the ioapic device can not be found in a qtest environment
when requesting "irq_interrupt_in ioapic" via the qtest socket.

By mirroring how the ioapic is added in i44ofx (hw/i440/pc_piix.c),
as a child of "q35," the device is able to be seen by qtest.
Signed-off-by: NJohn Snow <jsnow@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>