Inventory: PCIeDevice: add association to pcie_slot

Create association documentation to pcie slot from pcie devices.

Change-Id: I167aa18864572953bb5f7c7c3b7031d0b6046366
Signed-off-by: Willy Tu <wltu@google.com>
diff --git a/yaml/xyz/openbmc_project/Inventory/Item/PCIeDevice.interface.yaml b/yaml/xyz/openbmc_project/Inventory/Item/PCIeDevice.interface.yaml
index 54f0930..e4e4f84 100644
--- a/yaml/xyz/openbmc_project/Inventory/Item/PCIeDevice.interface.yaml
+++ b/yaml/xyz/openbmc_project/Inventory/Item/PCIeDevice.interface.yaml
@@ -293,3 +293,12 @@
       default: 0
       description: >
           The maximum number of PCIe lanes supported by the PCIe Device
+
+associations:
+    - name: upstream_pcie_slot
+      description: >
+          Objects that implement PCIeDevice can optionally implement the
+          upstream_pcie_slot association to provide a link back to a PCIe slot.
+      reverse_name: associated_pcie_device
+      required_endpoint_interfaces:
+        - xyz.openbmc_project.Inventory.Item.PCIeSlot