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

[Lucas Ramirez via llvm-commits]

https://github.com/lucas-rami commented:

Still need to review `RewriteScheduleStage::rewrite` but already left a bunch of small comments.

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