[llvm] [RISCV] Mark RVV stores and some loads as masked pseudo (PR #123106)

[Luke Lau via llvm-commits]

lukel97 wrote:

> And do we need some changes in RISCVVectorPeephole? Because I missed that when doing the same thing for `vcpop.m/vfirst.m`.

I think it RISCVVectorPeephole should be OK, since after c8ee1164bd6ae2f0a603c53d1d29ad5a3225c5cd we handle the no-passthru masked pseudos properly, which is what this PR had to change (and was made more explicit in ec5d17b58779e2fb08a7c9c706b2842586f71f78)

https://github.com/llvm/llvm-project/pull/123106