[SCSI] async: introduce 'async_domain' type

This is in preparation for teaching async_synchronize_full() to sync all
pending async work, and not just on the async_running domain.  This
conversion is functionally equivalent, just embedding the existing list
in a new async_domain type.

The .registered attribute is used in a later patch to distinguish
between domains that want to be flushed by async_synchronize_full()
versus those that only expect async_synchronize_{full|cookie}_domain to
be used for flushing.

[jejb: add async.h to scsi_priv.h for struct async_domain]
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Tested-by: Eldad Zack <eldad@fogrefinery.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
diff --git a/drivers/scsi/scsi_priv.h b/drivers/scsi/scsi_priv.h
index 13d74da..8f9a0cad 100644
--- a/drivers/scsi/scsi_priv.h
+++ b/drivers/scsi/scsi_priv.h
@@ -2,6 +2,7 @@
 #define _SCSI_PRIV_H
 
 #include <linux/device.h>
+#include <linux/async.h>
 #include <scsi/scsi_device.h>
 
 struct request_queue;
@@ -163,7 +164,7 @@
 static inline void scsi_autopm_put_host(struct Scsi_Host *h) {}
 #endif /* CONFIG_PM_RUNTIME */
 
-extern struct list_head scsi_sd_probe_domain;
+extern struct async_domain scsi_sd_probe_domain;
 
 /* 
  * internal scsi timeout functions: for use by mid-layer and transport