vboot2: Add common functions

This is the third of several CLs adding a more memory- and
code-efficient firmware verification library.

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

Change-Id: I3a5daa5438afc5598d3dfcf5a597ffb16eda8749
Signed-off-by: Randall Spangler <rspangler@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/200140
Reviewed-by: Bill Richardson <wfrichar@chromium.org>
7 files changed