s390/qdio: let drivers opt-out from Output Queue scanning

If a driver wants to use the new Output Queue poll code, then the qdio
layer must disable its internal Queue scanning. Let the driver select
this mode by passing a special scan_threshold of 0.

As the scan_threshold is the same for all Output Queues, also move it
into the main qdio_irq struct. This allows for fast opt-out checking, a
driver is expected to operate either _all_ or none of its Output Queues
in polling mode.

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/s390/include/asm/qdio.h

@@ -359,7 +359,7 @@ struct qdio_initialize {
 	qdio_handler_t *output_handler;
 	void (**queue_start_poll_array) (struct ccw_device *, int,
 					  unsigned long);
-	int scan_threshold;
+	unsigned int scan_threshold;
 	unsigned long int_parm;
 	struct qdio_buffer **input_sbal_addr_array;
 	struct qdio_buffer **output_sbal_addr_array;