[llvm] [AMDGPU] Exclude implicit uses and defs in SIInsertWaitcnts. NFC. (PR #108953)

[Stanislav Mekhanoshin via llvm-commits]

rampitec wrote:

So the assumption here an implicit VGPR use is never a real use.

https://github.com/llvm/llvm-project/pull/108953