vboot2: misc higher-level routines, part 2

I'm breaking the last chunk of vboot2 into smaller pieces as I add
tests.  This has the higher-level routines for verifying keyblock and
preamble.

BUG=chromium:370082
BRANCH=none
TEST=make clean && VBOOT2=1 COV=1 make

Change-Id: I82da9542c8857a3f89a85f206c9f5aecadf94a79
Signed-off-by: Randall Spangler <rspangler@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/203501
Reviewed-by: Bill Richardson <wfrichar@chromium.org>
4 files changed