mesa/st+vc4: Disable OES_texture_3D for PIPE_CAP_MAX_TEXTURE_3D_LEVELS==0.
This will be used for vc4, where incorrectly exposing 3D textures accounts for most of the GLES2 conformance failures it has. This leaves EXT_texture3d exposed in the (already non-conformant) GL2.1 support it exposes, which has always been a best-effort thing.