[components][drivers] Check macro "RT_USING_DFS" when using DFS relative method/functions.

components/drivers/serial/serial.c

@@ -48,6 +48,7 @@
 #include <posix_termios.h>
 #endif
 
+#ifdef RT_USING_DFS
 #ifdef RT_USING_DFS_DEVFS
 #include <dfs_posix.h>
 
@@ -209,7 +210,7 @@ const static struct dfs_file_ops _serial_fops =
     serial_fops_poll,
 };
 #endif
-
+#endif
 /*
  * Serial poll routines
  */

components/drivers/src/pipe.c

@@ -23,8 +23,10 @@
  */
 #include <rthw.h>
 #include <rtdevice.h>
+#if defined(RT_USING_DFS)
 #include <dfs_file.h>
 #include <dfs_posix.h>
+#endif
 
 #if defined(RT_USING_DFS) && defined(RT_USING_DFS_DEVFS)
 static int pipe_open(struct dfs_fd *fd)