[clang] [llvm] [NFC][HLSL] Move emitter out of AMDGPU.cpp (PR #133251)

[Jonathan Thackray via llvm-commits]

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

Thanks for creating this PR, LGTM (I wasn't able to do it earlier as one of my kids was ill, so away from laptop)

https://github.com/llvm/llvm-project/pull/133251