qdev: provide DEFINE_PROP_INT64()

qdev: provide DEFINE_PROP_INT64()

We have nearly all the stuff, but this one is missing. Add it in.

Am going to use this new helper for MigrationParameters fields, since
most of them are int64_t.

CC: Markus Armbruster <armbru@redhat.com>
CC: Eduardo Habkost <ehabkost@redhat.com>
CC: Marc-André Lureau <marcandre.lureau@redhat.com>
CC: Peter Xu <peterx@redhat.com>
CC: Juan Quintela <quintela@redhat.com>
CC: Marcel Apfelbaum <marcel@redhat.com>
CC: Eric Blake <eblake@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Marcel Apfelbaum <marcel@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <1500349150-13240-2-git-send-email-peterx@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>