[AMDGPU][InsertWaitCnts] Refactor some helper functions, NFC#161160

Pierre-vh merged 2 commits intomainllvm/llvm-project:mainfrom

users/pierre-vh/nfc-factor-out-helpers-insertwaitcntsllvm/llvm-project:users/pierre-vh/nfc-factor-out-helpers-insertwaitcntsCopy head branch name to clipboard