Make the serial driver framework work with CONFIG_SERIAL_MULTI enabled
diff --git a/include/serial.h b/include/serial.h
index 8c7b1c2..4880059 100644
--- a/include/serial.h
+++ b/include/serial.h
@@ -26,6 +26,13 @@
    || defined(CONFIG_405EP) || defined(CONFIG_MPC5xxx)
 extern struct serial_device serial0_device;
 extern struct serial_device serial1_device;
+#if defined(CFG_NS16550_SERIAL)
+extern struct serial_device eserial1_device;
+extern struct serial_device eserial2_device;
+extern struct serial_device eserial3_device;
+extern struct serial_device eserial4_device;
+#endif /* CFG_NS16550_SERIAL */
+
 #endif