livepatch/core: Support load and unload hooks

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8MGE6


CVE: NA

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The front-tools kpatch-build support load and unload hooks
in the older version and already changed to use pre/post
callbacks.

However, for livepatch based on stop machine consistency,
this callbacks will be called within stop_machine context if
we using it. This is dangerous because we can't known what
the user will do in the callbacks. It may trigger system
crash if using any function which internally might sleep.

Here we use the old load/unload hooks to allow user-defined
hooks. Although it's not good enough compared to pre/post
callbacks, it can meets user needs to some extent.
Of cource, this requires cooperation of kpatch-build tools.

Signed-off-by: Cheng Jian <cj.chengjian@huawei.com>
Signed-off-by: Wang ShaoBo <bobo.shaobowang@huawei.com>
Signed-off-by: Dong Kai <dongkai11@huawei.com>
Signed-off-by: Ye Weihua <yeweihua4@huawei.com>
Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>