Avoid using i64 types for vld1q_lane/vst1q_lane intrinsics.

The backend has to legalize i64 types by splitting them into two 32-bit pieces,
which leads to poor quality code.  If we produce code for these intrinsics that
uses one-element vector types, which can live in Neon vector registers without
getting split up, then the generated code is much better.  Radar 11998303.

llvm-svn: 161879