[llvm] RISCV: Replace most Specifier constants with relocation types (PR #138644)

[Sam Elliott via llvm-commits]

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

I am happy with this patch, and I trust you and @jrtc27 to come to a solution I will be happy with on the issue she saw.

(I'm going to be travelling, and don't want to block this patch once Jessica approves)

https://github.com/llvm/llvm-project/pull/138644