i965/miptree: Add support for window system images to create_for_dri_image

i965/miptree: Add support for window system images to create_for_dri_image

We want to start using create_for_dri_image for all miptrees created
from __DRIimage, including those which come from a window system.  In
order to allow for fast clears to still work on window system buffers,
we need to allow for creating aux surfaces.

Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
Reviewed-by: Chad Versace <chadversary@chromium.org>