Add message registry entry for successful fw update staging

Add an event log in redfish when fw completed writing to staging area
during firmware update.

Tested:
Update BMC firmware
POST: https://<BMC_IP>/redfish/v1/UpdateService/
      with <BMC_Update_Capsule> binary file
After BMC reboots with successful update check for Event log in
Redfish
Command: GET: https://<BMC_IP>/redfish/v1/Systems/system/LogServices/
              EventLog/Entries
Response:
{
      "@odata.id": "/redfish/v1/Systems/system/LogServices/EventLog/
                    Entries/1595803968",
      "@odata.type": "#LogEntry.v1_4_0.LogEntry",
      "Created": "2020-07-26T22:52:48+00:00",
      "EntryType": "Event",
      "Id": "1595803968",
      "Message": "BMC firmware update to version 00.74 staged
                  successfully.",
      "MessageArgs": [
        "BMC",
        "00.74"
      ],
      "MessageId": "OpenBMC.0.1.FirmwareUpdateStaged",
      "Name": "System Event Log Entry",
      "Severity": "OK"
    },

Signed-off-by: Chalapathi Venkataramashetty <chalapathix.venkataramashetty@intel.com>
Change-Id: I62aad007c7fc8d311a351d1c5ec4e84d6b4a77ad
diff --git a/redfish-core/include/registries/openbmc_message_registry.hpp b/redfish-core/include/registries/openbmc_message_registry.hpp
index 236002e..042a83a 100644
--- a/redfish-core/include/registries/openbmc_message_registry.hpp
+++ b/redfish-core/include/registries/openbmc_message_registry.hpp
@@ -29,7 +29,7 @@
     "0.1.0",
     "OpenBMC",
 };
-constexpr std::array<MessageEntry, 182> registry = {
+constexpr std::array<MessageEntry, 183> registry = {
     MessageEntry{
         "ADDDCCorrectable",
         {
@@ -464,6 +464,16 @@
                      {"string", "string", "string"},
                      "None.",
                  }},
+    MessageEntry{"FirmwareUpdateStaged",
+                 {
+                     "Indicates a firmware update has staged successfully.",
+                     "%1 firmware update to version %2 staged successfully.",
+                     "OK",
+                     "OK",
+                     2,
+                     {"string", "string"},
+                     "None.",
+                 }},
     MessageEntry{"FirmwareUpdateStarted",
                  {
                      "Indicates a firmware update has started.",