[llvm] [RISCV][WIP] Let RA do the CSR saves. (PR #90819)

[Michael Maitland via llvm-commits]

michaelmaitland wrote:

> In my original patch there was a hack related to emission of CFI's and the CFI inserter. I am trying to get rid of that we can get rid of the RISCV CFI inserter.

I **strongly** support this direction. Copying the target agnostic CFI inserter as a target specific CFI inserter is likely not a viable direction. If we need to add some target specific logic to the CFI inserter, the we should use target hooks.

https://github.com/llvm/llvm-project/pull/90819