[x86] Switching the shuffle equivalence test to a variadic template was

[x86] Switching the shuffle equivalence test to a variadic template was
the wrong answer. We also got initializer lists which are *way* cleaner
for this kind of thing. Let's use those and make this a normal, boring
functionn accepting ArrayRef.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230004 91177308-0d34-0410-b5e6-96231b3b80d8