IDWT 5x3: generalize SSE2 version for AVX2

IDWT 5x3: generalize SSE2 version for AVX2

Thanks to our macros that abstract SSE use, the functions can use
AVX2 when available (at compile time)

This brings an extra 23% speed improvement on bench_dwt in 64bit builds
with AVX2 compared to SSE2.