bdb: Add secrets library

The secrets library clears, extends, and derives secrets which are used
by vboot SoC.

BUG=chrome-os-partner:51907
BRANCH=tot
TEST=make runtests

Change-Id: I38c93fd450364792cebc942694f848e10d0e9502
Signed-off-by: Daisuke Nojiri <dnojiri@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/349252
Reviewed-by: Randall Spangler <rspangler@chromium.org>
7 files changed