firmware: Refactor and clean up ec_sync

Previously, the EC software sync process called VbDisplayScreen() from
several function calls deep.  Refactor software sync so that the UI
decisions are at a higher level (in ec_sync_all.c) and isolated from
the low-level EC software sync functionality (in ec_sync.c).

This is one in a series of changes which are more clearly separating
out the UI, to make it easier to support multiple UI across a range of
devices.

BUG=chromium:611535
BRANCH=none
TEST=make runtests; build_packages --board=reef chromeos-firmware; boot reef

Change-Id: I40597abeb5b0cc8f5d8fc2098e4acbed4bf59bf6
Signed-off-by: Randall Spangler <rspangler@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/411921
Reviewed-by: Shelley Chen <shchen@chromium.org>
11 files changed