[A57FPLoadBalancing] Remove support for vector types

Vector MUL/MLAs have tied operands, which gives us extra constraints
that we currently can't handle. Instead of silently doing the wrong
thing, remove support to be readded later properly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217690 91177308-0d34-0410-b5e6-96231b3b80d8