cpu-hotplug: export cpu_hotplug_enable/cpu_hotplug_disable

cpu-hotplug: export cpu_hotplug_enable/cpu_hotplug_disable

Hyper-V module needs to disable cpu hotplug (offlining) as there is no
support from hypervisor side to reassign already opened event channels
to a different CPU. Currently it is been done by altering
smp_ops.cpu_disable but it is hackish.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 32145c4677d2c46b9d877a33ae82c6fcacd002f9)

As hv driver depends on it
Orabug: 21886720
Signed-off-by: Jason Luo <zhangqing.luo@oracle.com>