[llvm] [RISCV] Add IsSignExtendingOpW to AMO*_W instructions. (PR #72349)

[Alex Bradbury via llvm-commits]

https://github.com/asb approved this pull request.

LGTM. I think there's an argument for adding IsSignExtendingOpW for instructions with that property even if it makes no difference in the current codegen pipeline. But happy to defer to your preference.

https://github.com/llvm/llvm-project/pull/72349