[SCSI] rework scsi_target allocation

The current target allocation code registeres each possible target
with sysfs; it will be deleted again if no useable LUN on this target
was found. This results in a string of 'target add/target remove' uevents.

Based on a patch by Hannes Reinecke <hare@suse.de> this patch reworks
the target allocation code so that only uevents for existing targets
are sent. The sysfs registration is split off from the existing
scsi_target_alloc() into a in a new scsi_add_target() function, which
should be called whenever an existing target is found. Only then a
uevent is sent, so we'll be generating events for existing targets
only.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

include/scsi/scsi_device.h

@@ -181,7 +181,8 @@ struct scsi_device {
 	sdev_printk(prefix, (scmd)->device, fmt, ##a)
 
 enum scsi_target_state {
-	STARGET_RUNNING = 1,
+	STARGET_CREATED = 1,
+	STARGET_RUNNING,
 	STARGET_DEL,
 };