[llvm] [AMDGPU] Create AMDGPUMnemonicAlias tablegen class (PR #89288)

[Jay Foad via llvm-commits]

https://github.com/jayfoad commented:

Interesting. I feel like this would need a further round of cleanups before I could see whether it's actually an improvement overall or not.

https://github.com/llvm/llvm-project/pull/89288