[llvm] [RISCV][GISel] Support G_ROTL/G_ROTR with Zbb. (PR #72825)

[Amara Emerson via llvm-commits]

aemerson wrote:

In general (doesn't have to be for this patch), could we have separate PRs for generic legalizer changes (with the MIR tests) and any target specific isel support? This would be a good exercise for the new LLVM blessed stacked PR support.

https://github.com/llvm/llvm-project/pull/72825