greybus: operation: use per-connection work queues

Replace the global operation work queue with per-connection work queues.

There is no need to keep operations strictly ordered across connections,
something which only adds unnecessary latency.

Tested-by: Rui Miguel Silva <rui.silva@linaro.org>
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
diff --git a/drivers/staging/greybus/connection.h b/drivers/staging/greybus/connection.h
index d8fbce4..6b40c4a 100644
--- a/drivers/staging/greybus/connection.h
+++ b/drivers/staging/greybus/connection.h
@@ -39,6 +39,8 @@
 	enum gb_connection_state	state;
 	struct list_head		operations;
 
+	struct workqueue_struct		*wq;
+
 	atomic_t			op_cycle;
 
 	void				*private;