livepatch: Introduce 'arch_klp_save_old_code'

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4UAQ1



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Introduce 'arch_klp_save_old_code' preparing for moving func_node
initializing codes out of stop_machine.

Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Reviewed-by: Kuohai Xu <xukuohai@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>