sharepool: 修复潜在的ABBA死锁

构造场景令维测打印/proc/sharepool/proc_stat和加入新组并发，可以发现如下ABBA死锁。

There is a ABBA deadlock in the process of sp_group_add_task and
proc_stat_show().

PROCESS A:
sp_group_add_task() acquire sp_group_sem write lock
->sp_init_proc_stat() acquire sp_spg_stat_sem write lock
PROCESS B:
proc_stat_show() acquire sp_spg_stat_sem read lock
->idr_proc_stat_cb() acquire sp_group_sem read lock

Here we choose the simplest way that acquires sp_group_sem and
sp_stat_sem read lock subsequently in proc_stat_show(), since it just
has effect on the process of debug feature.

测试步骤：

令N个进程并发地加入new group，同时cat /proc/sharepool/proc_stat尝试打印维测信息

测试现象：
出现死锁

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受影响版本排查(受影响/不受影响):
1.openEuler-22.03-LTS(5.10.0):受影响
2.openEuler-20.03-LTS-SP1(4.19.90):受影响
3.openEuler-20.03-LTS-SP2(4.19.90):受影响
4.openEuler-20.03-LTS-SP3(4.19.194):受影响

修复是否涉及abi变化(是/否)：
1.openEuler-22.03-LTS(5.10.0):否
2.openEuler-20.03-LTS-SP1(4.19.90):否
3.openEuler-20.03-LTS-SP2(4.19.90):否
4.openEuler-20.03-LTS-SP3(4.19.194):否

GVP openEuler / kernel

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GVPopenEuler / kernel

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