sched: cpu_power: enable ARCH_POWER

Heteregeneous ARM platform uses arch_scale_freq_power function
to reflect the relative capacity of each core

Change-Id: I7b8c9dfabb7a679229e563769f07a38690b217e5
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1341826026-6504-6-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>