[llvm] [AMDGPU] Add scheduling stage to rewrite MFMA from VGPR to AGPR (PR #149367)

[Jeffrey Byrnes via llvm-commits]

jrbyrnes wrote:

I had previously manually stacked this on https://github.com/llvm/llvm-project/pull/150711

The MFMA rewrite PR uses ArchVGPR pressure as both a condition for rewriting, and cost calculations. Thus, being able to distinguish between AVGPR pressure and ArchVGPR pressure is important for this to work as expected. However, since the VGPR MFMA is not used by default, I don't think we need to land these in order.

https://github.com/llvm/llvm-project/pull/149367