feat(tbbr): add image id for backup GPT

Add image identifier to access backup-GPT header and entry,
when we fail to get primary GPT header.

Currently we use only the primary gpt header, But we plan to
use backup GPT header in case our primary GPT header fails
verification or is corrupted.

Change-Id: I12eedd5d2a5cda21c64254d461d09d400d4edb30
Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>
1 file changed