debug_objects: add boot-parameter toggle to turn object debugging off again

While trying to debug why my Atom netbook is falling over booting
rawhide debug-enabled kernels, I stumbled across the fact that we've
been enabling object debugging by default. However, once you default it
to on, you've got no way to turn it back off again at runtime.

Add a boolean toggle to turn it off. I would just make it an int
module_param, however people may already expect the boolean enable
behaviour, so just add an analogue for disabling.

Signed-off-by: Kyle McMartin <kyle@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>