sign_official_build: loem support for firmware In order to support signing firmwares with loem keys, support taking in the firmware bundle unpacked. BUG=b:339024336 TEST=None BRANCH=None Signed-off-by: Benjamin Shai <bshai@google.com> Change-Id: Ibf4c1921599c1853415232eced26bd23f16d49ec Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/5519148 Reviewed-by: Julius Werner <jwerner@chromium.org>