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>
sched: clean up task_hot function

task_hot doesn't need the 'sched_domain' parameter, so remove it.

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