treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 248

Based on 1 normalized pattern(s):

  this file is released under the gpl v2

extracted by the scancode license scanner the SPDX license identifier

  GPL-2.0-only

has been chosen to replace the boilerplate/reference in 3 file(s).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexios Zavras <alexios.zavras@intel.com>
Reviewed-by: Allison Randal <allison@lohutok.net>
Reviewed-by: Armijn Hemel <armijn@tjaldur.nl>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190602204655.103854853@linutronix.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

kernel/power/poweroff.c

+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * poweroff.c - sysrq handler to gracefully power down machine.
- *
- * This file is released under the GPL v2
  */
 
 #include <linux/kernel.h>

lib/klist.c

+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * klist.c - Routines for manipulating klists.
  *
  * Copyright (C) 2005 Patrick Mochel
  *
- * This file is released under the GPL v2.
- *
  * This klist interface provides a couple of structures that wrap around
  * struct list_head to provide explicit list "head" (struct klist) and list
  * "node" (struct klist_node) objects. For struct klist, a spinlock is

mm/interval_tree.c

+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * mm/interval_tree.c - interval tree for mapping->i_mmap
  *
  * Copyright (C) 2012, Michel Lespinasse <walken@google.com>
- *
- * This file is released under the GPL v2.
  */
 
 #include <linux/mm.h>