Will be used when adopting rounddown_pow_of_two.

Cc: Adrian Hunter
Cc: Borislav Petkov
Cc: David Ahern
Cc: Don Zickus
Cc: Frederic Weisbecker
Cc: Jiri Olsa
Cc: Mike Galbraith
Cc: Namhyung Kim
Cc: Paul Mackerras
Cc: Peter Zijlstra
Cc: Stephane Eranian
Link: http://lkml.kernel.org/n/tip-9m0tt5300q1ygv51hejjas82@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo