Revert r324903 "[AArch64] Refactor identification of SIMD immediates"

It caused "Cannot select: t33: f64 = AArch64ISD::FMOV Constant:i32<0>"
in Chromium builds. See PR36369.

> Get rid of icky goto loops and make the code easier to maintain (NFC).
>
> Differential revision: https://reviews.llvm.org/D42723

llvm-svn: 325034