I'd be inclined to refer to that as a "Cable Anchor", and they can come in a number of variations. One, as part of the backing plate like you show; two, cast as part of the lower fork leg (stanchion); three, a separate bracket that is sandwiched with the fender mounting bracket; plus others, I'm sure. These are just what come to mind that I've seen in the past. Any of them are viable, and the separate bracket that uses the fender mount might be the easiest to fabricate.
Nathan