[llvm] [RISCV][NFCI] Introduce Base for Pseudo Expansion Passes (PR #218170)

[Sam Elliott via llvm-commits]

lenary wrote:

I think it's clearer if all the atomic expand passes check the size, rather than just 3/4 of them. It's only done on builds with assertions anyway.

https://github.com/llvm/llvm-project/pull/218170