[clang] [RISCV] Add sched model for XiangShan-NanHu (PR #70232)

[Yingwei Zheng via cfe-commits]

dtcxzyw wrote:

> Can you separate out the basic processor definition (using NoSchedModel), and a patch which adds the scheduling model? We can at least get the processor definition landed while we iterate on the scheduling related pieces.
> 
> edit: For clarity, I'm requesting that the basic processor definition and test updates be made into its own pull request, and that this pull request be reserved for adding the schedule model on top.

Posted as #70294.

https://github.com/llvm/llvm-project/pull/70232