feat(fs): implement littlefs lfs.h driver support (#5562)

lv_conf_template.h

@@ -641,6 +641,12 @@
     #define LV_FS_MEMFS_LETTER '\0'     /*Set an upper cased letter on which the drive will accessible (e.g. 'A')*/
 #endif
 
+/*API for LittleFs. */
+#define LV_USE_FS_LITTLEFS 0
+#if LV_USE_FS_LITTLEFS
+    #define LV_FS_LITTLEFS_LETTER '\0'     /*Set an upper cased letter on which the drive will accessible (e.g. 'A')*/
+#endif
+
 /*LODEPNG decoder library*/
 #define LV_USE_LODEPNG 0