[llvm] [RISCV][llvm-exegesis] Add default Pfm cycle counter. (PR #121866)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

That should be reasonable enough for the purposes of validating the scheduling models. It's interesting that the noise seems so much higher than on x86 though.

https://github.com/llvm/llvm-project/pull/121866