scarlet: Enable DISCHARGE_ON_AC
scarlet: Enable DISCHARGE_ON_AC

BUG=b:68065301
BRANCH=none
TEST=1)'ectool chargecontrol discharge', verify charging stops
     2)'ectool chargecontrol normal', verify charging restarts

Change-Id: I95e6e545419fee678ace6a5bea7f902dfc8de242
Signed-off-by: Philip Chen <3ee404f9ef892bc3fda6e6a76e65843b5fa44db2@google.com>
Reviewed-on: https://chromium-review.googlesource.com/732043
Commit-Ready: Philip Chen <3ee404f9ef892bc3fda6e6a76e65843b5fa44db2@chromium.org>
Tested-by: Philip Chen <3ee404f9ef892bc3fda6e6a76e65843b5fa44db2@chromium.org>
Reviewed-by: Shawn N <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec