sched: Support kill boost for offline task

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8MF4R


CVE: NA

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If online tasks occupy 100% CPU resources, offline tasks can't be scheduled
since offline tasks are throttled, as a result, offline task can't timely
respond after receiving SIGKILL signal.

Signed-off-by: Zhang Qiao <zhangqiao22@huawei.com>
Signed-off-by: Wenyu Huang <huangwenyu5@huawei.com>