[llvm] [AArch64][GlobalISel] Basic SVE and fadd (PR #72976)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

Would this eventually work in SelectionDAGCompat.td?
```
def : GINodeEquiv<G_FADD_PRED, fadd>;
```

https://github.com/llvm/llvm-project/pull/72976