apic: kvm-apic: Fix crash due to access to freed memory region

kvm-apic.io_memory memory region had its parent set to NULL at
memory_region_init_io() time, so it ended up as a child in
 /unattached contaner.
As result when kvm-apic instance was deleted, the child property
 /unattached/kvm-apic-msi[XXX] contained a reference to
kvm-apic.io_memory address which was freed as part of kvm-apic.

Do the same as 'apic' and make kvm-apic instance the owner
of the memory region so that it won't end up in /unattached
and gets cleanly released along with related kvm-apic instance.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
