[llvm] [X86] Early exit MIR AMX passes when AMX is unused (PR #94989)

[via llvm-commits]

aengelke wrote:

Updating MIR tests is #94988 -- this was a bit more work than I expected (needs YAML infrastructure for X86FunctionInfo), so I split it out in a separate PR.

https://github.com/llvm/llvm-project/pull/94989