[llvm] [RISCV] Custom lower fixed length partial.reduce to zvqdotq (PR #141180)

[Philip Reames via llvm-commits]

preames wrote:

> Are there no tests for vqdotu?

Hadn't been for fixed vector since they were covered by scalable, but I added vqdotu and vqdotsu (not yet supported) cases.  

https://github.com/llvm/llvm-project/pull/141180