s390x/ap: Wire up the device request notifier interface

Let's wire up the device request notifier interface to handle device unplug
requests for AP.

Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
Link: https://lore.kernel.org/qemu-devel/20230530225544.280031-1-akrowiak@linux.ibm.com/


Signed-off-by: Cédric Le Goater <clg@redhat.com>