treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 506

Based on 1 normalized pattern(s):

  this software program is licensed subject to the gnu general public
  license gpl version 2 june 1991 available at http www fsf org
  copyleft gpl html

extracted by the scancode license scanner the SPDX license identifier

  GPL-2.0-only

has been chosen to replace the boilerplate/reference in 4 file(s).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Allison Randal <allison@lohutok.net>
Reviewed-by: Enrico Weigelt <info@metux.net>
Reviewed-by: Daniel German <dmg@turingmachine.org>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190604081207.687420463@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>