[llvm] [AMDGPU] Have VCC as a first-class member of the SGPR pool. (PR #173870)

[Ivan Kosarev via llvm-commits]

kosarev wrote:

> It seems the code should be updated to catch the new tuples, though. Will look into it.

We keep the new tuples reserved here, so any hazards should be irrelevant.

Rebased.

https://github.com/llvm/llvm-project/pull/173870