Support dumping Turin data structures and Milan data structures at the same time

[daym]

Right now, MemDfeSearchElement* cannot be correctly dumped into json because it's impossible to figure out using in-band information which of the struct definitions to use.

If we cannot find the information in an in-band way, we need to add an out-of-band mechanism so we can pass context to the serializer so amd-apcb can eventually decide which MemDfeSearchElement* definition to use depending on the context (processor generation or similar) that was passed.

See also oxidecomputer/amd-host-image-builder#191