[X86][AVX1] Combine concat_vectors(pshufd(x,c),pshufd(y,c)) -> vpermilps(concat_vectors(x,y),c)

Bitcast v4i32 to v8f32 and back again - it might be worth adding isel patterns for X86PShufd v8i32 on AVX1 targets like we did for X86Blendi to avoid the bitcasts?

llvm-svn: 365125