What does this PR do?

benchmarking xformer memory_efficient_attention implementation

Fixes # (issue)

Adds # (feature)

Before submitting

[ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
[ ] Did you read the contributor guideline?
[ ] Did you make sure to update the documentation with your changes? E.g. record bug fixes or new features in What's New. Here are the documentation guidelines
[ ] Did you build and run the code without any errors?
[ ] Did you report the running environment (NPU type/MS version) and performance in the doc? (better record it for data loading, model inference, or training tasks)
[ ] Did you write any new necessary tests?

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