[llvm] [AMDGPU] Max. WG size-induced occupancy limits max. waves/EU (PR #137807)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm approved this pull request.

I'm a little uneasy about depending so hard on amdgpu-lds-size, but it's probably OK to be overly optimistic if it's unset 

https://github.com/llvm/llvm-project/pull/137807