kevin / gru: Enabling charging at up to 20V
kevin / gru: Enabling charging at up to 20V

BUG=chrome-os-partner:54551
BRANCH=None
TEST=Manual on kevin. Verify negotiation to 20V when zinger is plugged.
Also verify "pd 0 dev 12" and "pd 0 dev 5" cause 12V/5V to be requested
from zinger.

Change-Id: I0298d535b791fa0c6f8ca077a6fd09a27e8ce77b
Signed-off-by: Shawn Nematbakhsh <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/353804
Commit-Ready: Shawn N <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Tested-by: Shawn N <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

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