[llvm] [AMDGPU] [SIFrameLowering] Use LiveRegUnits instead of LivePhysRegs (PR #65962)

[Christudasan Devadasan via llvm-commits]

cdevadas wrote:

Why not split them into two separate PRs and mention the generic patch's PR info in the second one (AMDGPU-specific)?


https://github.com/llvm/llvm-project/pull/65962