[llvm] [AMDGPU] Add AGPR pressure tracking (PR #214745)

[Shilei Tian via llvm-commits]

https://github.com/shiltian commented:

Most of the changes are mechanical. It looks fine to me, but IIRC we have the AV super RC. How do we differentiate them here?

https://github.com/llvm/llvm-project/pull/214745