zink: mark 2d-arrays as cube-compatible

OpenGL allows reinterpreting 2D array textures as cubemaps,
so we need to always set the cube-compatible flag for them.

This fixes a piglit test on Lavapipe.

Reviewed-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10913>