sched: Add a knob to disable the core_ctl

The CPU hotplug tests does not work with core_ctl compiled
statically into kernel. Provide an interface to disable
the hotplug by core_ctl.

Change-Id: I61ea36332f21e8f456bdfba8b89dd4d148020b61
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>