Integrate (un)realization of child buses with realization/unrealization
of the device hosting them. Code in device_unparent() is reordered for
unrealization of buses to work as part of device unrealization.
That way no changes need to be made to bus instantiation.
Signed-off-by: Bandan Das <bsd@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>