The ERR/WARN macros already print the function name.

On the subject of actually supporting software devices, we should probably
implement those by creating a software or reference adapter with appropriate
gl_info and pipe implementations and creating a device based on that.

Just make sure the texture is allocated, so we have something to attach. Note
also that context_apply_attachment_filter_states() runs under the GL lock, so
preloading resources is actually unsafe there.