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

[Pengcheng Wang via llvm-commits]

wangpc-pp wrote:

I just wonder why we didn't ask Spacemit guys to provide the schedule model. They have a compiler team but are not so active in upstream.

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