[clang] [RISCV] Add processor definition for XiangShan-NanHu (PR #70294)

[Yingwei Zheng via cfe-commits]

dtcxzyw wrote:

> LGTM in general, except one question: will zicbom and zicboz be in the final RTL?

You can find the full implementation of `zicbom` and `zicboz` here: https://github.com/OpenXiangShan/XiangShan/commit/ca18a0b47b0e4089fd0dd1c085091cb90bf98f25.
cc @poemonsense


https://github.com/llvm/llvm-project/pull/70294