enable users to select triton fa for MLA backend

[qli88]

[MISC] enable users to select Triton FA for MLA backend

[github-actions]

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[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @qli88.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[houseroad]

Btw, why close this one?

[qli88]

A new PR broke this again. It is now in #13718 and got approved.