[llvm] [RISCV][VLOPT] Add support for vfmerge.vfm and vfmv.v.f (PR #146692)

[Luke Lau via llvm-commits]

lukel97 wrote:

> Don't we also want the merge in getOperandLog2EEW? Going purely by analogy to how we have the integer versions.

Both merge opcodes are already in getOperandLog2EEW, so we already allowed reducing the vl of instructions that were used by vfmerge.vfm/vfmv.v.f IIUC

https://github.com/llvm/llvm-project/pull/146692