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

[Mikhail R. Gadelha via llvm-commits]

mikhailramalho wrote:

Folks, we wrote a probe to double-check all latencies in the scheduler and updated the latencies accordingly. We tested it on two different boards to confirm the numbers.

The only outlier was idiv/irem, which was reported to have a latency of 3-4 in our experiments, so we went with the worst-case value shown in the C908 manual. I added a TODO to revisit this later. 

I also included the latencies for clmul, clmulr, and clmulh, which were missing from the first version of this PR.

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