Make SVN in DPE's `DeriveContext` optional.

[zhalvorsen]

• Caliptra Version(s) - 1.3

DPE made a breaking change to the DeriveContext command by adding an SVN field at the end. To avoid making this a breaking change to Caliptra integrators, we should add some logic to make the SVN field optional within the INVOKE_DPE_* commands. If the command received is a DeriveContext command without an SVN field, we will extend the command with an SVN of 0.