virgl doesn't yet support anisotropic filtering so don't advertise it.
Fixes: a8987b88ff1d ("virgl: add driver for virtio-gpu 3D (v2)") Reviewed-by: Gert Wollny <gert.wollny@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11944>