panfrost: ASTC 3D texture support

I noticed that Piglit had tests for 3D ASTC, so decided to use them to find what "stretch factor" is required for correct rendering.

This doesn't expose GL_OES_texture_compression_astc, because that extension requires both HDR and 3D ASTC support, and I'm not sure what the best way to handle that is. But no GPU would support 3D ASTC but not 2D HDR ASTC, so putting the 3D formats in texture_mapping in st_extensions.c for exposing the OES extension should be safe.

I note that Gallium doesn't even have a way to expose HDR ASTC at the moment. Maybe we should use PIPE_CAP_ASTC or something, which could also being used for controlling whether to expose the OES extension.

Though I would be surprised if anything ever actually used 3D ASTC...