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

[Thorsten Schütt via llvm-commits]

tschuett wrote:

GlobalIsel has no splat_vector yet. I was hoping that https://github.com/llvm/llvm-project/pull/74502 would make progress.

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