[llvm] [X86] Fix optmasks handling for AVX10.1-256 (PR #73074)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 approved this pull request.

LGTM on the `llvm-exegesis` side.

I don't think @LebedevRI is active in the project anymore, so getting a review from him might be difficult. If you want someone else to sign off on the `llvm-exegesis` side, @legrosbuffle and @gchatelet are the de facto codeowners.

https://github.com/llvm/llvm-project/pull/73074