ARM: dts: stm32: Ping IWDG on exit from PSCI suspend code

Make sure the OS would not get any spurious IWDG pretimeout IRQ
right after the system wakes up. This may happen in case the SoC
got woken up by another source than the IWDG pretimeout and the
pretimeout IRQ arrived immediately afterward, but too late to be
handled by the suspend main loop. In case either of the IWDG is
enabled, ping it first and then return to the OS.

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
Reviewed-by: Igor Opaniuk <igor.opaniuk@foundries.io>