[llvm] [AArch64] Don't try to vectorize fixed point to fp narrowing conversion (PR #130665)

[Pranav Kant via llvm-commits]

pranavk wrote:

Rebased. If tests pass, I will merge this. 

Thank you for reviewing and other patches (cost-model, and GISel changes). 

https://github.com/llvm/llvm-project/pull/130665