mach-msm: dyn_hotplug: Change method of online/offline cores

Fixes cpufreq stats breakage.

Signed-off-by: Stratos Karafotis <stratosk@semaphore.gr>
mach-msm: dyn_hotplug: Use enabled flag to protect enable/disable ops

Signed-off-by: Stratos Karafotis <stratosk@semaphore.gr>