sched: set sched_mc_power_savings to 2

This tunable provides serious power saving improvements similar to the power savings of hotplugging cores. Since we are using interactive governor by default, we're always using 2 cores at any time. Thus, we can benefit from this as this feature packs tasks together and try to bind them to cpu0, which in theory will let cpu1 idle longer, thus improving battery life.

Signed-off-by: zwliew <zhaoweiliew@gmail.com>