iris: Allow GPU-based uploads of ASTC textures

iris: Allow GPU-based uploads of ASTC textures

ISL recently started allowing linear ASTC surfaces to be created. With
that in place, iris can perform GPU-based uploads to ASTC textures in
the same way it does so with other compressed surfaces.

We're not aware of any reason to continue special-casing ASTC texture
uploads, so we get rid of the code which does so.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13881>