Revert "[FastISel][AArch64] Don't fold instructions too aggressively into the memory operation."

Quentin pointed out that this is not the correct approach and there is a better and easier solution.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216632 91177308-0d34-0410-b5e6-96231b3b80d8