platform/x86: simatic-ipc: use extra module loading for watchdog

We recently introduced a way to name additional modules to load for each
device. Use that instead of wdtmode to load the watchdog module. This
patch does not change behaviour, it is just style.

Signed-off-by: Henning Schild <henning.schild@siemens.com>
Link: https://lore.kernel.org/r/20230713144832.26473-4-henning.schild@siemens.com


Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>