DPE: Support cert_id as optional argument

For DeriveContext command, currently cert-id is handled as a mandatory argument.
Add support to handle it as an optional parameter.

Signed-off-by: Maulik Patel <maulik.patel@arm.com>
Change-Id: I6e823f5c1cae9eaeeebd549db3202dbe18b73e6e
2 files changed