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

[Thorsten Schütt via llvm-commits]

tschuett wrote:

```
   %v8:_(<2 x s64>) = G_BUILD_VECTOR %0(s64), %1(s64)
```
A build vector could be mixed between integer and float.

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