[llvm] [RISCV] Add scheduler definitions for SpacemiT-X60 (PR #137343)

[Philip Reames via llvm-commits]

https://github.com/preames commented:

This looks general reasonable, and I agree that for a black box schedule model the right threshold is to use observed performance.  

I'm going to run through (in a second pass) the available data for this core, and cross check the model.  Forthcoming shortly.

https://github.com/llvm/llvm-project/pull/137343