[llvm] [RISCV Add some vsetvli insertion test cases with vmv.s.x+reduction. NFC (PR #75544)

[Philip Reames via llvm-commits]

https://github.com/preames approved this pull request.

LGTM

For the record, the difference between integer and float is very weird here.  

https://github.com/llvm/llvm-project/pull/75544