[llvm] [AMDGPU] When allocating VGPRs, VGPR spills are not part of the prologue (PR #109439)

[via llvm-commits]

alex-t wrote:

> I have tested exactly the same change myself as an alternative to the #108596 the change has passed PSDB but it only run on MI200. Unfortunately, it causes blender barbershop scene rendering to hang on Navi21. That is why I did not published the PR for it. I am currently trying to find out the reason for the hang.

The blender hang on my Navi21 was due to the old/incompatible runtime. So, we can go with this fix.

https://github.com/llvm/llvm-project/pull/109439