[llvm] [Exegesis][RISCV] Add RISCV support for llvm-exegesis (PR #89047)

[via llvm-commits]

AnastasiyaChernikova wrote:

@legrosbuffle @mshockwave @michaelmaitland @topperc @boomanaiden154 @gchatelet I answered all the comments, please take a look

https://github.com/llvm/llvm-project/pull/89047