st/mesa: require RGBA2, RGB4, and RGBA4 to be renderable

If the driver does not support rendering to these formats but does
support texturing, we can end up in incompatibilities between textures
and renderbuffers that are then copied to.

Fixes KHR-GL45.copy_image.functional on nvc0

Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Cc: 19.0 <mesa-stable@lists.freedesktop.org>
(cherry picked from commit cbd1ad61)