vt82c686: Clean up use of cannot_instantiate_with_device_add_yet

vt82c686: Clean up use of cannot_instantiate_with_device_add_yet

A VT82C686B southbridge has multiple functions.  We model each
function as a separate qdev.  One of them need some special wiring set
up in mips_fulong2e_init() to work: the ISA bridge at 05.0.

The IDE controller at 05.1 (via-ide) has always had
cannot_instantiate_with_device_add_yet set, but there is no obvious
reason why device_add could not work for them.  Drop it.

Signed-off-by: Markus Armbruster <[email protected]>
Reviewed-by: Peter Maydell <[email protected]>
Signed-off-by: Andreas Färber <[email protected]>