[llvm] [RISCV] Remove RVInstV2. NFC (PR #177901)

[Craig Topper via llvm-commits]

topperc wrote:

> The simplification looks good, but I don't know if `RVInstVX` is proper because these two instruction are not actually `VX` instruction like other `.vx`s. Maybe we can add a class that inherits from `RVInstVX`?

RVInstVX class provides a field named `rs1` and dependency on VL, VTYPE. Those are correct for this instruction.

The things I'm more concerned about are vcpop.v and vfirst.v having their destination named `vd` instead of `rd`. And vmv.x.s and vfmv.f.s having an incorrect dependency on VL.

https://github.com/llvm/llvm-project/pull/177901