platform/chrome: cros_ec_typec: Register port partner

Register (and unregister) the port partner when a connect (and
disconnect) is detected.

Co-developed-by: Jon Flatley <jflat@chromium.org>
Signed-off-by: Prashant Malani <pmalani@chromium.org>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>