genirq: Add missing SPDX identifiers

Add SPDX identifiers to files

 - which contain an explicit license boiler plate or reference

 - which do not contain a license reference and were not updated in the
   initial SPDX conversion because the license was deduced by the scanners
   via EXPORT_SYMBOL_GPL as GPL2.0 only.

[ tglx: Moved adding identifiers from the patch which removes the
  	references/boilerplate ]
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Link: https://lkml.kernel.org/r/20180314212030.668321222@linutronix.de

kernel/irq/chip.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 1992, 1998-2006 Linus Torvalds, Ingo Molnar
  * Copyright (C) 2005-2006, Thomas Gleixner, Russell King

kernel/irq/cpuhotplug.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * Generic cpu hotunplug interrupt migration code copied from the
  * arch/arm implementation

kernel/irq/debugfs.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright 2017 Thomas Gleixner <tglx@linutronix.de>
  *

kernel/irq/devres.c

+// SPDX-License-Identifier: GPL-2.0
 #include <linux/module.h>
 #include <linux/interrupt.h>
 #include <linux/device.h>

kernel/irq/dummychip.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 1992, 1998-2006 Linus Torvalds, Ingo Molnar
  * Copyright (C) 2005-2006, Thomas Gleixner, Russell King

kernel/irq/generic-chip.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * Library implementing the most common irq chip callback functions
  *

kernel/irq/handle.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 1992, 1998-2006 Linus Torvalds, Ingo Molnar
  * Copyright (C) 2005-2006, Thomas Gleixner, Russell King

kernel/irq/ipi.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2015 Imagination Technologies Ltd
  * Author: Qais Yousef <qais.yousef@imgtec.com>

kernel/irq/irq_sim.c

+// SPDX-License-Identifier: GPL-2.0+
 /*
  * Copyright (C) 2017 Bartosz Golaszewski <brgl@bgdev.pl>
  *

kernel/irq/irqdesc.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 1992, 1998-2006 Linus Torvalds, Ingo Molnar
  * Copyright (C) 2005-2006, Thomas Gleixner, Russell King

kernel/irq/irqdomain.c

+// SPDX-License-Identifier: GPL-2.0
+
 #define pr_fmt(fmt)  "irq: " fmt
 
 #include <linux/acpi.h>

kernel/irq/manage.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 1992, 1998-2006 Linus Torvalds, Ingo Molnar
  * Copyright (C) 2005-2006 Thomas Gleixner

kernel/irq/msi.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2014 Intel Corp.
  * Author: Jiang Liu <jiang.liu@linux.intel.com>

kernel/irq/pm.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2009 Rafael J. Wysocki <rjw@sisk.pl>, Novell Inc.
  *

kernel/irq/timings.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2016, Linaro Ltd - Daniel Lezcano <daniel.lezcano@linaro.org>
  *