vboot2: Add routines to load and verify kernel keyblock

These are slightly more complex than the firmware versions, because
they need to deal with developer-signed keyblocks and keyblock flags.

BUG=chromium:487699
BRANCH=none
TEST=make -j runtests

Change-Id: I682c14ddfe729984f2629dfbe66750e5cd5ab75e
Signed-off-by: Randall Spangler <rspangler@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/272541
Reviewed-by: Daisuke Nojiri <dnojiri@chromium.org>
8 files changed