[llvm] [RISCV] Fix and refactor Zvk sched classes (PR #86519)

[Pengcheng Wang via llvm-commits]

https://github.com/wangpc-pp approved this pull request.

LGTM.
I think all the comments have been addressed? Maybe you need to reword the description.

https://github.com/llvm/llvm-project/pull/86519