[llvm] [RISCV] Don't allow '-' after 'ra' in Zcmp/Xqccmp register list. (PR #134182)

[Sam Elliott via llvm-commits]

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

LGTM

I wonder if the easiest way to restructure is to have a function `parseSingleRegisterOrRange` which we can invoke (up to) twice, depending on what range it got to?

https://github.com/llvm/llvm-project/pull/134182