PCIeDevice: change the Device Type to enum values

As defined in the Redfish [1], the DeviceType property can be
MultipleFunction/Retimer/Simulated/SingleFunction. Therefore, this
commit changes the type of DeviceType from string to enum values.

[1] https://redfish.dmtf.org/schemas/v1/PCIeDevice.v1_19_0.json

Change-Id: Ie752cf858f36957bb1eccda0afc3cf4073828f52
Signed-off-by: Thang Tran <thuutran@amperecomputing.com>
diff --git a/yaml/xyz/openbmc_project/Inventory/Item/PCIeDevice.interface.yaml b/yaml/xyz/openbmc_project/Inventory/Item/PCIeDevice.interface.yaml
index 8826a9d..2d85e3f 100644
--- a/yaml/xyz/openbmc_project/Inventory/Item/PCIeDevice.interface.yaml
+++ b/yaml/xyz/openbmc_project/Inventory/Item/PCIeDevice.interface.yaml
@@ -5,9 +5,11 @@
 
 properties:
     - name: DeviceType
-      type: string
+      type: enum[self.DeviceTypes]
+      default: "Unknown"
       description: >
-          Indicates if the device is MultiFunction or SingleFunction.
+          Indicates if the device type is MultiFunction/Retimer/Simulated or
+          SingleFunction.
     - name: GenerationInUse
       type: enum[xyz.openbmc_project.Inventory.Item.PCIeSlot.Generations]
       default: "Unknown"
@@ -298,6 +300,27 @@
           property is not known due to some unknown reason, like hardware
           failure. The value of 0 indicates that the link is not active.
 
+enumerations:
+    - name: DeviceTypes
+      description: >
+          Possible Device Type
+      values:
+          - name: MultiFunction
+            description: >
+                Indicates if the device is MultiFunction
+          - name: Retimer
+            description: >
+                Indicate if the device is Retimer
+          - name: Simulated
+            description: >
+                Indicates if the device is Simulated
+          - name: SingleFunction
+            description: >
+                Indicates if the device is Single Function
+          - name: Unknown
+            description: >
+                Indicates if the device is Unknown
+
 associations:
     - name: upstream_pcie_slot
       description: >