[llvm] [RISCV][GISEL] Add IRTranslation for shufflevector on scalable vector types (PR #80378)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> How would you otherwise distinguish between integer and float splats? If a splat vector only gets an immediate?

There's no need to, but you can always inspect the operands. In fact, I think we should get rid of G_FCONSTANT altogether and just adds unnecessary hassle 

https://github.com/llvm/llvm-project/pull/80378