Fan, Item: add cooling association

Create association documentation between Fan and Item.

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: Ifc3f38958c00f432a741774dbf570f39dd817966
diff --git a/yaml/xyz/openbmc_project/Inventory/Item.interface.yaml b/yaml/xyz/openbmc_project/Inventory/Item.interface.yaml
index 0326595..d74db10 100644
--- a/yaml/xyz/openbmc_project/Inventory/Item.interface.yaml
+++ b/yaml/xyz/openbmc_project/Inventory/Item.interface.yaml
@@ -41,3 +41,10 @@
           - 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