[llvm] [RISCV] computeKnownBits - add support for RISCVISD::VECREDUCE_ADD_VL (PR #210493)

[Luke Lau via llvm-commits]

https://github.com/lukel97 commented:

Looks like this needs a test. Are you able to add one?

https://github.com/llvm/llvm-project/pull/210493