Add conditional macro LV_USE_GROUP to more GROUP related singles:

- LV_SIGNAL_CONTROL
- LV_SIGNAL_GET_EDITABLE

src/lv_widgets/lv_dropdown.c

@@ -968,6 +968,7 @@ static lv_res_t lv_dropdown_signal(lv_obj_t * ddlist, lv_signal_t sign, void * p
         if(ext->page) lv_obj_refresh_style(ext->page, LV_STYLE_PROP_ALL);
     }
     else if(sign == LV_SIGNAL_CONTROL) {
+#if LV_USE_GROUP
         char c = *((char *)param);
         if(c == LV_KEY_RIGHT || c == LV_KEY_DOWN) {
             if(ext->page == NULL) {
@@ -992,10 +993,13 @@ static lv_res_t lv_dropdown_signal(lv_obj_t * ddlist, lv_signal_t sign, void * p
             ext->sel_opt_id = ext->sel_opt_id_orig;
             lv_dropdown_close(ddlist);
         }
+#endif
     }
     else if(sign == LV_SIGNAL_GET_EDITABLE) {
+#if LV_USE_GROUP
         bool * editable = (bool *)param;
         *editable       = true;
+#endif
     }
 
     return res;