[llvm] [GISEL] G_SPLAT_VECTOR can take a splat that is larger than the vector element (PR #86974)

[Michael Maitland via llvm-commits]

michaelmaitland wrote:

> Assuming that this is again for patterns, but G_SPLAT_VECTOR(G_TRUNC(s128)) should suffice during legalisation?

This is for patterns and for equivalence to SelectionDAG ISD::SPLAT_VECTOR.

https://github.com/llvm/llvm-project/pull/86974