SoftwareInventory: Implement Bios Related Item

Was a TODO here with the code commented out.

Bios was implemented here:
https://github.com/openbmc/bmcweb/commit/d82a3acd1abc04a13f90cef5234416c3e18da0e1



Tested: Ran validator
curl -k https://${bmc}/redfish/v1/UpdateService/FirmwareInventory/9f75c5ad
{
  "@odata.id": "/redfish/v1/UpdateService/FirmwareInventory/9f75c5ad",
  "@odata.type": "#SoftwareInventory.v1_1_0.SoftwareInventory",
  "Description": "Host image",
  "Id": "9f75c5ad",
  "Members@odata.count": 1,
  "Name": "Software Inventory",
  "RelatedItem": [
    {
      "@odata.id": "/redfish/v1/Systems/system/Bios"
    }
  ],

Change-Id: Ifa6148731582cdc7f177e38b19f02fea966738fc
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>