kobject: add SPDX identifiers to all kobject files

It's good to have SPDX identifiers in all files to make it easier to
audit the kernel tree for correct licenses.

Update the kobject files files with the correct SPDX license identifier
based on the license text in the file itself.  The SPDX identifier is a
legally binding shorthand, which can be used instead of the full boiler
plate text.

This work is based on a script and data from Thomas Gleixner, Philippe
Ombredanne, and Kate Stewart.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/kobject.h

+// SPDX-License-Identifier: GPL-2.0
 /*
  * kobject.h - generic kernel object infrastructure.
  *

include/linux/kobject_ns.h

+// SPDX-License-Identifier: GPL-2.0
 /* Kernel object name space definitions
  *
  * Copyright (c) 2002-2003 Patrick Mochel

lib/kobject.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * kobject.c - library routines for handling generic kernel objects
  *

lib/kobject_uevent.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * kernel userspace event delivery
  *

samples/kobject/kobject-example.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * Sample kobject implementation
  *

samples/kobject/kset-example.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * Sample kset and ktype implementation
  *