sched: clean up cpu_load update

Since we don't decay the rq->cpu_load, so we don't need the
pending_updates. But we still want update rq->rt_avg, so
still keep rq->last_load_update_tick and func __update_cpu_load.

After remove the load_idx, in the most of time the source_load is
equal to target_load, except only when source cpu is idle. At that
time we force set the cpu_load is 0(in update_cpu_load_nohz).
So we still left cpu_load in rq.

Signed-off-by: Alex Shi <alex.shi@linaro.org>
sched: bias to target cpu load to reduce task moving

Task migration happens when target just a bit less then source cpu load.
To reduce such situation happens, aggravate the target cpu load with
sd->imbalance_pct/100 in wake_affine.

In find_idlest/busiest_group, change the aggravate to local cpu only
from old fuzzy aggravation.

Signed-off-by: Alex Shi <alex.shi@linaro.org>