smart_grid: introduce /proc/pid/smart_grid_level

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I7ZBSR


CVE: NA

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Now, we can use /pro/pid/smart_grid_level to {read,set} task current qos
level.

This allows to determine the scope of dynamic partitioning of the task
in smart_grid.

SCHED_GRID_QOS_TASK_LEVEL was defined different QoS level. The lower number
has the higher priority. (E.g. 0 was the highest).

Signed-off-by: Yipeng Zou <zouyipeng@huawei.com>