There is no need for `revb_w` to reverse bytes for each 32-bit word. All the callers only care about the lower 32-bit word. This reimplement `revb_w` so that it only reverses bytes in lower 32-bit word and sign-extends the result. This makes `revb_w_w` duplicate. And the new `revb_w` will also emit less instructions than `revb_w_w`.