accel/habanalabs: prevent sending heartbeat before events are enabled

After the heartbeat mechanism is now expanded to be used also
for EQ health check, we shouldn't send heartbeat messages
to FW before driver allow events to be received from FW.

Because if the driver will send two heartbeats before it enables
events to be received from FW, then the EQ health check
will fail and reset the device.

Signed-off-by: farah kassabri <fkassabri@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>