dm: at91: Add driver model support for the serial driver

Add driver model support while retaining the existing legacy code. This
allows the driver to support boards that have converted to driver model
as well as those that have not.

Signed-off-by: Simon Glass <sjg@chromium.org>

arch/arm/include/asm/arch-at91/atmel_serial.h

@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) 2014 Google, Inc
+ *
+ * SPDX-License-Identifier:     GPL-2.0+
+ */
+
+#ifndef _ATMEL_SERIAL_H
+#define _ATMEL_SERIAL_H
+
+/* Information about a serial port */
+struct atmel_serial_platdata {
+	uint32_t base_addr;
+};
+
+#endif