LF-3296-2 watchdog: sbsa_gwdt: add shutdown hook to driver

commit d1331b9bb16c5318fc8a7b6831136c79c116f8d9 from
git://source.codeaurora.org/external/qoriq/qoriq-components/linux

Kexec maybe need more time than timeout of wdt(sbsa)
which will reset the system.
So it is necessary to add shutdown hook to disable the
wdt when run kexec.

Signed-off-by: Zhao Qiang <qiang.zhao@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>
Signed-off-by: Meng Li <Meng.Li@windriver.com>