debugobjects: add boot parameter default value

Impact: add .config driven boot parameter default value

Right now debugobjects can only be activated if the debug_objects
boot parameter is passed in via the boot command line.

Make this more convenient (and randomizable) by also providing
a .config method. Enable it by default. (DEBUG_OBJECTS itself
is default-off)

Signed-off-by: Ingo Molnar <mingo@elte.hu>