Support both legacy and new uboot.cnt file format

AUM should be able to work with both legacy and new u-boot, and their uboot.cnt respective file formats. Otherwise AUM consider the file is corrupted and triggers a rollback.
This commit allows to update AUM in a first step, work with the current u-boot before upgrading it.

Signed-off-by: Frédéric Danis frederic.danis@collabora.com