Add TD Info as Initialization Header

[yuehtingchen]

TDX VMs require additional launch time configurations for better flexibility

• Adds td_info as an optional header in the IGVM file to store TDX specific configurations
• Add xfam as a parameter in td_info to specify extended processor feature enablement
• Validate td_info compatibility mask specifies TDX platform

[chris-oo]

Is this really optional if it impacts the measurement of the guest? It's optional in the sense of "if you don't specify this, the VMM may choose whatever value it likes" correct?

[yuehtingchen]

Yes. It's optional in the sense that the IGVM file should load even if you don't specify these fields. I don't think all guests care if the measurements are different across different hosts, so some guests may choose not to specify these fields.