cpu/amd: Update/Add license headers

These license headers were either not compliant with the coreboot
standard or were missing completely.

Change-Id: I0c46ad9ba7f3d950b3eff96ee6e9c36acbf1a3a5
Signed-off-by: Damien Roth <yves.r.roth@gmail.com>
Reviewed-on: https://review.coreboot.org/13288
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

src/cpu/amd/agesa/heapmanager.c

@@ -1,3 +1,16 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * 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
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
 
 #include "AGESA.h"
 #include "amdlib.h"