sched/numa: Rename nr_running and break out the magic number

mainline inclusion
from mainline-v5.11-rc1
commit abeae76a
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I40C8N
CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=abeae76a47005aa3f07c9be12d8076365622e25c



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

This is simply a preparation patch to make the following patches easier
to read. No functional change.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20201120090630.3286-2-mgorman@techsingularity.net


Signed-off-by: Zheng Zucheng <zhengzucheng@huawei.com>
Reviewed-by: Chen Hui <judy.chenhui@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>