drivers/entropy: stm32: fix inter-core race condition

On STM32WB and dual-core STM32H7 MCUs, the RNG peripheral is shared
between the cores and its access is protected by a hardware semaphore.
Locking was not performed in the current entropy driver, leading to a
race condition when multiple cores concurrently used the RNG. This
commit implements the necessary logic for locking the HSEM during entropy
generation on multi-core STM32 MCUs. It also reconfigures the RNG in case
the configuration was changed by the other core, as this can happen e.g
on STM32WB MCUs.

Signed-off-by: Thomas Altenbach <taltenbach@witekio.com>