Scalar block layout doesn't allow anything that our memory load/store vectorizer
couldn't create on its own. So I assume whatever reason there was to only
expose this feature on GFX7+ was incorrect or ended up being fixed.
Passes vkcts in CI on tahiti.
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35279>