performance: add power scheduler option

the power scheduler allows the cpu to group tasks on a core, until it
reaches its maximum load and switches on the next core.

this is an attempt to save battery, as it uses the whole capacity of the
cores, until it turns on the next core.
but this also sacrifices power.

0 for disabled, 1 for balanced, 2 for aggressive.

Change-Id: Ie9c0e5956fd53048ef80de6c125dce62a039c221