Fan, Item: add cooling association

Create association documentation between Fan and Item.

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: Ifc3f38958c00f432a741774dbf570f39dd817966

yaml/xyz/openbmc_project/Inventory/Item.interface.yaml

@@ -41,3 +41,10 @@ associations:
           - inventory
       required_endpoint_interfaces:
           - xyz.openbmc_project.Sensor.Value
+    - name: cooled_by
+      description: >
+          Objects that implement Item can optionally implement the
+          'cooled_by' association to provide a link to one or more fans.
+      reverse_name: cooling
+      required_endpoint_interfaces:
+          - xyz.openbmc_project.Inventory.Item.Fan

yaml/xyz/openbmc_project/Inventory/Item/Fan.interface.yaml

@@ -1,2 +1,11 @@
 description: >
     Implement to provide Fan attributes.
+
+associations:
+    - name: cooling
+      description: >
+          Objects that implement Fan can optionally implement the
+          'cooling' association to provide a link back to a Item.
+      reverse_name: cooled_by
+      required_endpoint_interfaces:
+          - xyz.openbmc_project.Inventory.Item

yaml/xyz/openbmc_project/Inventory/Item/README.md

@@ -19,3 +19,4 @@ to Redfish schemas and then indicate the system topology.
 Document ObjectMapper association forward and reverse names as follows:
 * Item and Item: [containing, contained_by]
 * Sensor.Value and Bmc: [monitoring, monitored_by]
+* fan and item: [cooling, cooled_by]