kselftest: Add test for core sched prctl interface

mainline inclusion
from mainline-v5.14-rc1
commit 9f269900
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5OOWG
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9f26990074931bbf797373e53104216059b300b1



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Provides a selftest and examples of using the interface.

[peterz: updated to not use sched_debug]
Signed-off-by: Chris Hyser <chris.hyser@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Don Hiatt <dhiatt@digitalocean.com>
Tested-by: Hongyu Ning <hongyu.ning@linux.intel.com>
Tested-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20210422123309.100860030@infradead.org


Signed-off-by: Lin Shengwang <linshengwang1@huawei.com>
Reviewed-by: lihua <hucool.lihua@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>