sched: cpufreq: Adds a field cpu_power in the task_struct

cpu_power has been added to keep track of amount of power each task is
consuming. cpu_power is updated whenever stime and utime are updated for
a task. power is computed by taking into account the frequency at which
the current core was running and the current for cpu actively
running at hat frequency.

Bug: 21498425
Change-Id: Ic535941e7b339aab5cae9081a34049daeb44b248
Signed-off-by: Ruchi Kandoi <kandoiruchi@google.com>
Git-commit: 94877641f6b6ea17aa335729f548eb5647db3e3e
Git-repo: https://android.googlesource.com/kernel/msm/


Signed-off-by: Nirmal Abraham <nabrah@codeaurora.org>