[llvm] [AMDGPU] Add another SIFoldOperands instance after shrink (PR #67878)

[Jay Foad via llvm-commits]

jayfoad wrote:

If this goes in, as a follow up, could try removing `SIShrinkInstructions::foldImmediates`? It ought to be redundant.

https://github.com/llvm/llvm-project/pull/67878