[Feature request] RISC-V CMO support

I understand that Rocket Chip currently can support hardware prefetching when used with https://github.com/ucb-bar/bar-fetchers IPs in Chipyard.

It could also be useful to implement https://github.com/riscv/riscv-CMOs/blob/master/specifications/cmobase-v1.0.pdf to support software prefetch instructions

Start by reading the RISC-V CMO base specification and the Rocket Chip codebase, then compare its existing hardware-prefetching relationship with the bar-fetchers IPs used in Chipyard. Define the required software prefetch instructions and the affected Rocket Chip integration points; done means the specified CMO support is implemented and verified against the specification.

Written by the indexing model from the issue text.