[PATCH] aarch64: Improve codegen of AdvSIMD atan(2)(f)

[Wilco Dijkstra]

Hi Joana,

> Load the polynomial evaluation coefficients into 2 vectors and use lanewise MLAs.
> 8% improvement in throughput microbenchmark on Neoverse V1.

OK - pushed (needed an extra return at the end).

Cheers,
Wilco