[Code Clean] Clarify once_flag setting for kernel autotune module

[JamesLim-sy]

PR types

Function optimization

PR changes

Others

Describe

• Replace the std::once_flag outside the auto_tune class into the auto_tune class for code clarification.

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Sorry to inform you that 5c9aaf7's CIs have passed for more than 7 days. To prevent PR conflicts, you need to re-run all CIs manually.

[paddle-ci-bot[bot]]

Sorry to inform you that 66db14c's CIs have passed for more than 7 days. To prevent PR conflicts, you need to re-run all CIs manually.