[llvm] [AMDGPU] Replace hardcoded register class IDs with [[#]] (NFC) (PR #185402)

[Christudasan Devadasan via llvm-commits]

cdevadas wrote:

> This should be absolute now that MIR supports symbolic classes, pending bulk test updates

The PR stack starting with #186796 addresses the issue better. I will close my PRs. 

https://github.com/llvm/llvm-project/pull/185402