[SCSI] Add target alloc/destroy callbacks to the host template

This gives the HBA driver notice when a target is created and
destroyed to allow it to manage its own target based allocations
accordingly.

This is a much reduced verson of the original patch sent in by
James.Smart@Emulex.com

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index c018020..63c91dd 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -154,7 +154,9 @@
 	unsigned int		id; /* target id ... replace
 				     * scsi_device.id eventually */
 	unsigned long		create:1; /* signal that it needs to be added */
-	unsigned long		starget_data[0];
+	void 			*hostdata; /* available to low-level driver */
+	unsigned long		starget_data[0]; /* for the transport */
+	/* starget_data must be the last element!!!! */
 } __attribute__((aligned(sizeof(unsigned long))));
 
 #define to_scsi_target(d)	container_of(d, struct scsi_target, dev)