m_option: add UPDATE_VO flag

This will allow reiniting the VO when more options are changed without
hardcoding them in options.c

Also reinit the VO when changing --gpu-debug and --gpu-sw.

video/out/gpu/context.c

@@ -216,6 +216,7 @@ const struct m_sub_options ra_ctx_conf = {
         {0}
     },
     .size = sizeof(struct ra_ctx_opts),
+    .change_flags = UPDATE_VO,
 };
 
 static struct ra_ctx *create_in_contexts(struct vo *vo, const char *name,