[llvm] [AMDGPU][NFCI] Decouple actual register encodings from HWEncoding values. (PR #69452)

[Joe Nash via llvm-commits]

https://github.com/Sisyph commented:

Can you please improve the documentation about what does HWEncoding actually mean on the AMDGPU target? And also document the meaning of EncValues?

https://github.com/llvm/llvm-project/pull/69452