soc/intel_adsp: ipc: initialize semaphore in driver init

The ipc driver device data (struct intel_adsp_ipc_data) contains a
semaphore. Upon device init, the device data is zeroed out. This is safe
for other fields, but the semaphore should be properly initialized
before use.

This lack of initialization leads to a system crash when CONFIG_POLL is
enabled (e.g. to enable CONFIG_SHELL), IPC driver handles an interrupt
and executes k_sem_give() on a uninitialized semaphore object. This will
eventually lead to null dereference in z_handle_obj_poll_events().

Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>