While there is an encoding for it in VUZP, the result of that is undefined,
so we should avoid it. Define the instruction as a pseudo for VTRN.32
instead, as the ARM ARM indicates.
rdar://11222366
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154511 91177308-0d34-0410-b5e6-96231b3b80d8