[llvm] [AMDGPU]: Accept constant zero bytes in v_perm OrCombine (PR #66533)

[Jeffrey Byrnes via llvm-commits]

jrbyrnes wrote:

Just rebase for https://github.com/llvm/llvm-project/commit/3115ad8980e7d36adca95b5449db8ebf9bd94bf2 , still need to address comments.

https://github.com/llvm/llvm-project/pull/66533