[llvm] [LLVM] Update llvm-mca / MCA maintainers (PR #131187)

[Aiden Grossman via llvm-commits]

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

LGTM. Thanks for working on keeping this up to date!

I want to update/add maintainers for `llvm-exegesis`, but need to coordinate with Clement and Guillaume first to see what's up on their end.

https://github.com/llvm/llvm-project/pull/131187