[llvm] [AArch64] Keep floating-point conversion in SIMD (PR #147707)

[Guy David via llvm-commits]

guy-david wrote:

Thanks for the suggestions, I'll try the bitcast route and see where it leads.
As for the different types of FCVT*, I'm guessing that the additional inserts and extracts prevented them from kicking in? I'll write a commit that excludes those.

https://github.com/llvm/llvm-project/pull/147707