[llvm] [RISCV] Support select/merge like ops for bf16 vectors when have Zvfbfmin (PR #91936)

[Nico Weber via llvm-commits]

nico wrote:

Looks like this breaks tests: http://45.33.8.238/linux/139855/step_11.txt

Please take a look and revert for now if it takes a while to fix.

https://github.com/llvm/llvm-project/pull/91936