watchdog: Convert GPL 2.0 notice to SPDX identifier

Convert the boilerplate to SPDX license identifier. While at it, also
move SPDX identifier for drivers/watchdog/rtd119x_wdt.c to the top of
file (as in other files).

Cc: Ray Lehtiniemi <rayl@mail.com>,
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Deepak Saxena <dsaxena@plexity.net>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Jonas Jensen <jonas.jensen@gmail.com>
Cc: Sylver Bruneau <sylver.bruneau@googlemail.com>
Cc: Denis Turischev <denis@compulab.co.il>
Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Ray Lehtiniemi <rayl@mail.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lkml.kernel.org/r/20230517072140.1086660-2-bagasdotme@gmail.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>