image_verify: Support full image

The code only supports verify the static.mtd.tar, but not
static.mtd.all.tar.

This change adds the signature verify for the full tarball.

Tested: Update .static.mtd.all.tar with Redfish API OK.
        Update .static.mtd.tar with Redfish API OK.

Signed-off-by: Henry Tian <tianxiaofeng@bytedance.com>
Signed-off-by: Lei YU <yulei.sh@bytedance.com>
Change-Id: I58a47d76ef090644cc1e870077f438b8768f6aa9
2 files changed