add: lv_conf.h添加g_lvgl_flash_time声明

components/lvgl/lv_conf.h

@@ -59,6 +59,8 @@
 #define LV_DISP_DEF_REFR_PERIOD      30      /*[ms]*/
 #endif
 
+extern unsigned int g_lvgl_flash_time;
+
 /* Dot Per Inch: used to initialize default sizes.
  * E.g. a button with width = LV_DPI / 2 -> half inch wide
  * (Not so important, you can adjust it to modify default sizes and spaces)*/