treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 220

Based on 1 normalized pattern(s):

  distributed under the gnu gpl license version 2

extracted by the scancode license scanner the SPDX license identifier

  GPL-2.0-only

has been chosen to replace the boilerplate/reference in 1 file(s).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Reviewed-by: Alexios Zavras <alexios.zavras@intel.com>
Reviewed-by: Steve Winslow <swinslow@gmail.com>
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190528171439.854676954@linutronix.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/idr.h

+/* SPDX-License-Identifier: GPL-2.0-only */
 /*
  * include/linux/idr.h
  * 
  * 2002-10-18  written by Jim Houston jim.houston@ccur.com
  *	Copyright (C) 2002 by Concurrent Computer Corporation
- *	Distributed under the GNU GPL license version 2.
  *
  * Small id to pointer translation service avoiding fixed sized
  * tables.