[llvm-branch-commits] [RISCV] Port RISCVMergeBaseOffset to NewPM (PR #235250)

[Aiden Grossman via llvm-branch-commits]

https://github.com/boomanaiden154 created https://github.com/llvm/llvm-project/pull/235250

Standard NewPM pass porting.

- Remove opt suffix from name given it's somewhat redundant.
- Change to static methods with plumbing MRI/ST given an Impl class
  didn't some worth it.