[llvm] [AMDGPU] Add user flag to set min/max number of AGPRs. (PR #216800)

[Shilei Tian via llvm-commits]

shiltian wrote:

I don't think it's a good idea to special case occupancy >= 2. This seems like just treating the symptoms instead of the root cause. I wonder why it is a good idea not to use AGPR when occupancy >= 2?

https://github.com/llvm/llvm-project/pull/216800