drivers: watchdog: stm32H7 window watchdog during debug

This commit is controlling the WWDG during the Stop mode in debug.
WWDG1 is frozen while the core is in Debug mode, setting the bit
of the DBGMCU APB3 peripheral freeze register (DBGMCU_APB3FZ1)
for the stm32H7 soc devices.

Signed-off-by: Francois Ramu <francois.ramu@st.com>