openocd: src: replace the GPL with eCos exception 2.0 license tag

Add the license exception text in the license pool.
Add the exception chapter in license-rules.txt
Replace the boilerplate with the SPDX tag.

The SPDX tag on files *.c is incorrect, as it should use the C99
single line comment using '//'. But current checkpatch doesn't
allow C99 comments, so keep using standard C comments, by now.

Change-Id: Ied513b7c9c0722ed2a9c11dbdff3fbf59f1b41ce
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/7061
Tested-by: jenkins

src/flash/nand/ecc.c

@@ -1,3 +1,5 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later WITH eCos-exception-2.0 */
+
 /*
  * This file contains an ECC algorithm from Toshiba that allows for detection
  * and correction of 1-bit errors in a 256 byte block of data.
@@ -10,30 +12,6 @@
  *                         Toshiba America Electronics Components, Inc.
  *
  * Copyright (C) 2006 Thomas Gleixner <tglx at linutronix.de>
- *
- * This file 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; either version 2 or (at your option) any
- * later version.
- *
- * This file 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.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program.  If not, see <http://www.gnu.org/licenses/>.
- *
- * As a special exception, if other files instantiate templates or use
- * macros or inline functions from these files, or you compile these
- * files and link them with other works to produce a work based on these
- * files, these files do not by themselves cause the resulting work to be
- * covered by the GNU General Public License. However the source code for
- * these files must still be made available in accordance with section (3)
- * of the GNU General Public License.
- *
- * This exception does not invalidate any other reasons why a work based on
- * this file might be covered by the GNU General Public License.
  */
 
 #ifdef HAVE_CONFIG_H