treewide: Replace GPLv2 boilerplate/reference with SPDX - gpl-2.0_56.RULE (part 1)

Based on the normalized pattern:

    this file is licensed under the terms of the gnu general public
    license version 2 this program is licensed as is without any warranty
    of any kind whether express or implied

extracted by the scancode license scanner the SPDX license identifier

    GPL-2.0-only

has been chosen to replace the boilerplate/reference.

Reviewed-by: Allison Randal <allison@lohutok.net>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>