Change config_deactivate(9) to always unset the DVF_ACTIVE flag so

Change config_deactivate(9) to always unset the DVF_ACTIVE flag so
that drivers can check for this flag to know they have to stop doing
any hardware access and release their reference.

While here makes the ca_activate() function optional and propagates
DVACT_DEACTIVATE to the children of a device that do not implement this
interface like it is done during suspend/resume.

ok uebayasi@, deraadt@