mtd: ubi: Update license header for ubi-media.h file

[Lionel DEBIEVE]

Hi,

I'm currently working on a first stage bootloader using UBI support for 
NAND boot. My concern is about the ubi-media.h file. This header file 
contains UBI structures described in specification (ie 
http://www.linux-mtd.infradead.org/doc/ubi.html.) and only contains 
structures and some defines, there is no kernel API inside.

To develop UBI driver support for first stage bootloader such as Arm 
Trusted Firmware, it could be possible to use Thomas Gleixner existing 
development made in U-Boot (a lightweight driver for U-Boot SPL) that 
allows**with restricted functionality to boot from UBI. Thomas wrote the 
driver in dual license (GPLv2 and BSD3-Clause) but it includes the 
ubi-media.h file. So, I'm currently blocked because the file ubi-media.h 
is only GPLV2.

I'd like you to check if it could be possible to change license header 
(GPLV2) to dual license as Thomas's driver (GPLv2 and BSD3-Clause) to 
allow UBI’s developer using that common structure file in different 
primary bootloader, helping UBI to be the standard solution for raw NAND 
management at any boot stages.*
*
In that scope, I would also update header to the following SPDX license 
header:

/* SPDX-License-Identifier: (GPL-2.0+ OR BSD-3-Clause) */
/*
  * Copyright (C) International Business Machines Corp., 2006
  * Authors: Artem Bityutskiy (Битюцкий Артём)
  *          Thomas Gleixner
  *          Frank Haverkamp
  *          Oliver Lohmann
  *          Andreas Arnez
*/

BR,
Lionel/
/