va: fail context create if driver does not support video

not all drivers support this, and forcing them to implement stubs
is not how gallium works

cc: mesa-stable

Reviewed-by: David Rosca <david.rosca@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31736>

src/gallium/frontends/va/context.c

@@ -204,6 +204,10 @@ VA_DRIVER_INIT_FUNC(VADriverContextP ctx)
    if (!drv->vscreen)
       goto error_screen;
 
+   /* video cannot work if these are not supported */
+   if (!drv->vscreen->pscreen->get_video_param || !drv->vscreen->pscreen->is_video_format_supported)
+      goto error_pipe;
+
    drv->pipe = pipe_create_multimedia_context(drv->vscreen->pscreen);
    if (!drv->pipe)
       goto error_pipe;