src/mainboard: Add and update license headers

This change adds and updates headers in all of the mainboard files that
had missing or unrecognized headers.  After this goes in, we can turn on
lint checking for headers in all mainboard directories.

Change-Id: Ibe038a8f7468253b21fd2ac90c045d0c9cc89dfc
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/26568
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
diff --git a/src/mainboard/sifive/hifive-unleashed/mainboard.c b/src/mainboard/sifive/hifive-unleashed/mainboard.c
index bfc4d6e..e7f7a40 100644
--- a/src/mainboard/sifive/hifive-unleashed/mainboard.c
+++ b/src/mainboard/sifive/hifive-unleashed/mainboard.c
@@ -3,9 +3,9 @@
  *
  * Copyright (C) 2018 Jonathan Neuschäfer
  *
- * This software is licensed under the terms of the GNU General Public
- * License version 2, as published by the Free Software Foundation, and
- * may be copied, distributed, and modified under those terms.
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of