[llvm] Codegen - AMDGPU Subtarget FIXMES (PR #205499)

[Jay Foad via llvm-commits]

jayfoad wrote:

> NFC: move getMaxNumWorkGroups out of the subtarget into AMDGPUBaseInfo, refactored properly.

Split that out into a separate NFC PR please.

https://github.com/llvm/llvm-project/pull/205499