[Redfish] Fix incorrect mapping of dbus and Redfish API strings for BootSource

- "Cd" should be mapped to "xyz.openbmc_project.Control.Boot.Source.Sources.DVD"
- Adding mapping "Usb" to "xyz.openbmc_project.Control.Boot.Source.Sources.Removable"

Tested:
PATCH /redfish/v1/Systems/system HTTP/1.1
{
	"Boot": {
        "BootSourceOverrideTarget": "Cd" (or "Usb")
    }
}
Response:
{
    "@Message.ExtendedInfo": [
        {
            "@odata.type": "/redfish/v1/$metadata#Message.v1_0_0.Message",
            "Message": "Successfully Completed Request",
            "MessageArgs": [],
            "MessageId": "Base.1.4.0.Success",
            "Resolution": "None",
            "Severity": "OK"
        }
    ]
}

GET /redfish/v1/Systems/system HTTP/1.1
Response:
...
   Boot:
   {
	...
	"BootSourceOverrideTarget": "Cd",  (or "Usb")
	...
   }
...

Signed-off-by: Jennifer Lee <jennifer1.lee@intel.com>
Change-Id: Ib5f69fe93d45b4012c089bd48e484ef978a4e57a
diff --git a/redfish-core/lib/systems.hpp b/redfish-core/lib/systems.hpp
index 8019d8c..a76f2c4 100644
--- a/redfish-core/lib/systems.hpp
+++ b/redfish-core/lib/systems.hpp
@@ -468,7 +468,7 @@
         return "Hdd";
     }
     else if (dbusSource ==
-             "xyz.openbmc_project.Control.Boot.Source.Sources.ExternalMedia")
+             "xyz.openbmc_project.Control.Boot.Source.Sources.DVD")
     {
         return "Cd";
     }
@@ -477,6 +477,11 @@
     {
         return "Pxe";
     }
+    else if (dbusSource ==
+             "xyz.openbmc_project.Control.Boot.Source.Sources.Removable")
+    {
+        return "Usb";
+    }
     else
     {
         return "";
@@ -531,12 +536,16 @@
     }
     else if (rfSource == "Cd")
     {
-        return "xyz.openbmc_project.Control.Boot.Source.Sources.ExternalMedia";
+        return "xyz.openbmc_project.Control.Boot.Source.Sources.DVD";
     }
     else if (rfSource == "Pxe")
     {
         return "xyz.openbmc_project.Control.Boot.Source.Sources.Network";
     }
+    else if (rfSource == "Usb")
+    {
+        return "xyz.openbmc_project.Control.Boot.Source.Sources.Removable";
+    }
     else
     {
         return "";