vboot: Notify EC of current boot mode

Notify EC of boot mode, i.e. normal, developer or recovery.
This is necessary for battery firmware updates.

BUG=chrome-os-partner:24741
BRANCH=ToT
TEST=Verified on glimmer.

Change-Id: I1613ede34b4a929d1e8114fb519861f349377e94
Signed-off-by: Sheng-Liang Song <ssl@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/214273
Reviewed-by: Randall Spangler <rspangler@chromium.org>
4 files changed