sched: bias to target cpu load to reduce task moving

Old code considers the bias in source/target_load already. but still
use imbalance_pct as last check in idlest/busiest group finding. It is
also a kind of redundant job. If we can consider the source/target
bias, we'd better not use imbalance_pct again.

After cpu_load array removed, it is nice time to unify the target bias
consideration. So I move the imbalance_pct from last check to live using.

Signed-off-by: Alex Shi <alex.shi@linaro.org>
sched/noh_full: don't return 0 load in nohz_full idle exit

We are not always 0 when update nohz cpu load, after nohz_full enabled.
But current code still treat the cpu as idle. that is incorrect.
Fix it to use correct cpu_load.

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

After change to sched_avg, the cpu load in idle exit was decayed.
So, it maybe near zero if waking a long time sleep task, or, a near
non-decay load if waking a new forked task. Then, we can use it to
reflect the cpu load, don't need to pretend 0.

Signed-off-by: Alex Shi <alex.shi@linaro.org>
sched: clean up source_load/target_load

Don't need 'rq' variable now. and only heavier load if BA_BIAS.

Signed-off-by: Alex Shi <alex.shi@linaro.org>
sched: clean up weighted_cpuload

weighted_cpuload is used instead of source_load() when !idx.
Now idx is always 0. so unify the usage to soruce_load. That make
code more readable.

Signed-off-by: Alex Shi <alex.shi@linaro.org>
sched: remove rq->cpu_load and rq->nr_load_updates

The cpu_load is the copy of rq->cfs.runnable_load_avg. And it updated
on time. So we can use the latter directly. Thus saved 2 rq variables:
cpu_load and nr_load_updates.

Signed-off-by: Alex Shi <alex.shi@linaro.org>
sched: rename update_*_cpu_load

Since we have no cpu_load update, rename the related functions:
s/update_idle_cpu_load/update_idle_rt_avg/
s/update_cpu_load_nohz/update_rt_avg_nohz/
s/update_cpu_load_active/update_avg_load_active/

No functional change.

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