dt-bindings: watchdog: stm32-iwdg: Document interrupt and wakeup properties

The watchdog IP can generate pre-timeout interrupt and can be used as
a wake up source. Document both properties.

Signed-off-by: Marek Vasut <marex@denx.de>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240705115052.116705-1-marex@denx.de


Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>