cert_create: extend Secure partition support for tbbr CoT

with sha 0792dd7, support to generate certificate for Secure
Partitions was added for dualroot CoT only, this patch extends
this support for tbbr CoT.

Signed-off-by: Manish Pandey <manish.pandey2@arm.com>
Change-Id: I451c0333536dd1cbe17861d454bdb0dc7a17c63f
6 files changed