sched: Introduce priority load balance for CFS

euleros inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5HF3M


CVE: NA

Reference: NA

--------------------------------

Add new sysctl interface:
`/proc/sys/kernel/sched_prio_load_balance_enabled`

 0: default behavior
 1: enable priority load balance for qos scheduler

For tasks co-location with qos scheduler, when CFS do load balance,
it is reasonable to prefer migrating online(Latency Sensitive) tasks.
So the CFS load balance can be changed to below:

1) `cfs_tasks` list is owned by online tasks.
2) Add new `cfs_offline_tasks` list which is owned by offline tasks.
3) Prefer to migrate the online tasks of `cfs_tasks` list to dst rq.

Signed-off-by: zhangsong <zhangsong34@huawei.com>
Reviewed-by: Zhang Qiao <zhangqiao22@huawei.com>
--------------------------------
V2->V3:
- remove skip_migrate_task for load balance
V1->V2:
- remove setting cpu shares for offline cgroup

 Conflicts:
	kernel/sched/sched.h