[clang] [llvm] [RISCV] Add processor definition for XiangShan-KunMingHu-V2R2 (PR #123193)

[Pengcheng Wang via cfe-commits]

wangpc-pp wrote:

LGTM in general, but I have a question here: can you clarify the naming strategy? The name used in `-mcpu` is `xiangshan-kunminghu`, which corresponds to the `V2R2` version now apparently. Then, will there be `V2R3`/`V3R2`/...? If so, what should we use in `-mcpu`?

https://github.com/llvm/llvm-project/pull/123193