[llvm] [AArch64] Fix #94909: Optimize vector fmul(sitofp(x), 0.5) -> scvtf(x, 2) (PR #141480)

[JP Hafer via llvm-commits]

jph-13 wrote:

I will take a look at the tablegen impls. Maybe that will help me understand why I am having issues with half too. 

https://github.com/llvm/llvm-project/pull/141480