[llvm] [RISCV] Preserve tail agnostic policy in some vector peepholes (PR #105788)

[Luke Lau via llvm-commits]

lukel97 wrote:

Posted https://github.com/llvm/llvm-project/pull/106108 to showcase the regressions that this fixes (the code changes themselves are very scrappy, please ignore!)

https://github.com/llvm/llvm-project/pull/105788