[dfs] add new option (DFS_FILESYSTEM_TYPES_MAX) for DFS

components/dfs/KConfig

@@ -14,7 +14,11 @@ if RT_USING_DFS
     config DFS_FILESYSTEMS_MAX
         int "The maximal number of mounted file system"
         default 2
-    
+
+    config DFS_FILESYSTEM_TYPES_MAX
+        int "The maximal number of file system type"
+        default 2
+
     config DFS_FD_MAX
         int "The maximal number of opened files"
         default 4