egl: add note about missing $plat_teardown

Some platforms are missing a proper teardown function. Add a small TODO
to make it obvious.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>

src/egl/drivers/dri2/egl_dri2.c

@@ -998,6 +998,7 @@ dri2_display_destroy(_EGLDisplay *disp)
       dri2_teardown_wayland(disp);
       break;
    default:
+      /* TODO: add teardown for other platforms */
       break;
    }