configuration: mtmitchell: Support MGM with Item.BMC interface

Support the management board with the `xyz.openbmc_project.Inventory
.Item.BMC` interface to label the hardware type.

Change-Id: Idd78e1976ff2ac7bd1dc854fdf7e2fabf442efa0
Signed-off-by: Thang Q. Nguyen <thang@os.amperecomputing.com>
diff --git a/configurations/mtmitchell_bmc.json b/configurations/mtmitchell_bmc.json
index dd3f726..227d78f 100644
--- a/configurations/mtmitchell_bmc.json
+++ b/configurations/mtmitchell_bmc.json
@@ -128,6 +128,7 @@
         "FieldReplaceable": false,
         "HotPluggable": false
     },
+    "xyz.openbmc_project.Inventory.Item.BMC": {},
     "xyz.openbmc_project.Inventory.Item.NetworkInterface": {
         "MACAddress": "$BOARD_INFO_AM1"
     }