vl: Create (most) objects before creating chardev backends

vl: Create (most) objects before creating chardev backends

Some types of object must be created before chardevs, other types of
object must be created after chardevs. As such there is no option but
to create objects in two phases.

This takes the decision to create as many object types as possible
right away before anyother backends are created, and only delay
creation of those few which have an explicit dependency on the
chardevs. Hopefully the set which need delaying will remain small
over time.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>