[llvm] [AMDGPU][True16][CodeGen] readfirstlane for vgpr16 copy to sgpr32 (PR #137848)

[Joe Nash via llvm-commits]

Sisyph wrote:

I would recommend not opening a new PR for a new version of a patch. It only serves to make finding previous discussion harder, and messing up people's subscribe/unsubscribe selections. The previous PR should be updated.

https://github.com/llvm/llvm-project/pull/137848