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

[Matt Arsenault via llvm-commits]

https://github.com/arsenm requested changes to this pull request.

This change to the class structure should not be made. SGPR_* should remain being numbered SGPRs only. We have the additional SReg_32* classes for including the unnumbered registers 

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