vboot2: Add workbuf functions

We'll try breaking this up into smaller pieces.  This one's pretty
small - just the work buffer utility functions.

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

Change-Id: I4c417438053c155d6f7f9725552066e9b059951c
Signed-off-by: Randall Spangler <rspangler@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/201141
6 files changed