sched: Influence cpu_power based on max_freq and efficiency

Update cpu_power metric of a cpu by accounting its efficiency and
max_freq factors. cpu_power is defined such that "least" performing
cpu (one with lowest efficiency and max_freq factor) gets cpu_power of
1024. Note that no single CPU may have both the lowest efficiency and
lowest max_freq. All CPUs will still have cpu_power values relative to
this combination receiving a cpu_power of 1024 however.

cpu_power differs from capacity metric of a cpu by accounting
real-time task activity.

Change-Id: I255d3ad80d8bc8237b9ffb8f6e7c0dc4c44ec10f
Signed-off-by: Srivatsa Vaddagiri <vatsa@codeaurora.org>