[llvm] [AMDGPU] Remove implicit defs on expanded mov64 pseudos (PR #190379)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

These super register implicit defs are semi necessary. If you need the liveness of the full super register, you need it to avoid prematurely clobbering other lanes of the register between the components. However, in these particular cases I can't see how this would go wrong in practice, particularly given the inputs are immediates 

https://github.com/llvm/llvm-project/pull/190379