Unified build support for multi-firmware signing

Unified builds break down multiple firmware images for each model;
however, the signing script didn't have support for this.

This updates the signing script to iterate over all models in a unified
build and sign each firmware image separately.

BUG=chromium:734485
TEST=sign_official_build.sh recovery for reef and reef-uni
BRANCH=none

Change-Id: Ia2b5b8bd36ac77aeb7944362186d1d5739e6ff3d
Reviewed-on: https://chromium-review.googlesource.com/540131
Commit-Ready: C Shapiro <shapiroc@google.com>
Tested-by: C Shapiro <shapiroc@google.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Jason Clinton <jclinton@chromium.org>
1 file changed