migration: convert to NotifierWithReturn

migration: convert to NotifierWithReturn

Change all migration notifiers to type NotifierWithReturn, so notifiers
can return an error status in a future patch.  For now, pass NULL for the
notifier error parameter, and do not check the return value.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/1708622920-68779-4-git-send-email-steven.sistare@oracle.com
[peterx: dropped unexpected update to roms/seabios-hppa]
Signed-off-by: Peter Xu <peterx@redhat.com>