cpumask: export cpumask_any_but

Export cpumask_any_but() for module use. This will be used by drivers
such as intel_rapl to locate an active cpu on a socket.

Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>