Add handling for FRU prefixes

There are some FRU eeproms in the wild that use the custom field to
represent the MAC address, but prefix the mac itself with "MAC:"

Detect this case, and expose this as a new field MAC_<Previous
fieldname>.  This allows Entity-Manager to properly parse the MAC
address to fill into EthernetInterface and set the MAC address.

Tested: Boot a platform with this type of fru (P3809)
Observe that the MAC address is set correctly.  Introspecting DBUS shows
the mac field was added correctly

Change-Id: I03dbeebc41c8e589d7992b91d589f40e9e11f5c5
Signed-off-by: Ed Tanous <etanous@nvidia.com>
diff --git a/configurations/nvidia_bmc_p3809.json b/configurations/nvidia_bmc_p3809.json
index 1f9b91f..65686ea 100644
--- a/configurations/nvidia_bmc_p3809.json
+++ b/configurations/nvidia_bmc_p3809.json
@@ -9,5 +9,8 @@
     ],
     "Name": "BMC",
     "Probe": "xyz.openbmc_project.FruDevice({'PRODUCT_MANUFACTURER': 'NVIDIA', 'PRODUCT_PRODUCT_NAME': 'P3809-BMC'})",
-    "Type": "Board"
+    "Type": "Board",
+    "xyz.openbmc_project.Inventory.Item.NetworkInterface": {
+        "MACAddress": "$MAC_BOARD_INFO_AM2"
+    }
 }