WorkStruct: Separate delayable and non-delayable events.

Separate delayable work items from non-delayable work items be splitting them
into a separate structure (delayed_work), which incorporates a work_struct and
the timer_list removed from work_struct.

The work_struct struct is huge, and this limits it's usefulness.  On a 64-bit
architecture it's nearly 100 bytes in size.  This reduces that by half for the
non-delayable type of event.

Signed-Off-By: David Howells <dhowells@redhat.com>
diff --git a/include/linux/libata.h b/include/linux/libata.h
index abd2deb..5f04006 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -568,8 +568,8 @@
 	struct ata_host		*host;
 	struct device 		*dev;
 
-	struct work_struct	port_task;
-	struct work_struct	hotplug_task;
+	struct delayed_work	port_task;
+	struct delayed_work	hotplug_task;
 	struct work_struct	scsi_rescan_task;
 
 	unsigned int		hsm_task_state;