[llvm] [GlobalISel][AArch64] Legalize G_SPLAT_VECTOR (PR #114006)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

For legalization of G_SPLAT_VECTOR, the tests are sufficient. When we add combines, we can extend the tests.

https://github.com/llvm/llvm-project/pull/114006