Support Genoa Platform

[mkulke]

Current situation

Milan and Genoa use a different pair of ASK + ARK certificate chain. Milan is hardcoded (when requesting cert chain from AMD KDS). It makes for the time being, as the Azure CVM instances are Milan-based so far.

Impact

With the introduction of Genoa-Familiy instance types, KDS will be called with the wrong parameters fetched.

Ideal future situation

We provide forward compatibility for Genoa CPUs.

Implementation options

In the sev crate there is a platform detection heuristic (check which ASK signs the VCEK).

Additional information

This issue is mostly for tracking, it's not yet clear how CVM support would be implemented on Genoa instance types.