vboot2: add code to verify vb2_keyblock2

Now supports multiple signatures per keyblock.

And associated unit tests.

BUG=chromium:423882
BRANCH=none
TEST=VBOOT2=1 make runtests

Change-Id: I7f2ef216e3689a22ed86c34763f68345d4080e04
Signed-off-by: Randall Spangler <rspangler@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/227181
Reviewed-by: Bill Richardson <wfrichar@chromium.org>
3 files changed