Combine VGA discovery and registration.  Quirks can have dependencies
on BARs, so the quirks push out until after we've scanned the BARs.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Tested-by: Gerd Hoffmann <kraxel@redhat.com>