drivers: entropy: stm32 entropy driver add semaphore protection

Add a semaphore to protect the disable access to the RNG peripheral
when the PM is going to suspend mode.
The change does not affect other stm32 than CONFIG_SOC_SERIES_STM32WBX
or CONFIG_STM32H7_DUAL_CORE

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