platform/chrome: cros_ec_typec: Parse partner PD ID VDOs

Use EC_CMD_TYPE_DISCOVERY to retrieve and store the discovery data for
the port partner. With that data, update the PD Identity VDO values for
the partner, which were earlier not initialized.

Signed-off-by: Prashant Malani <pmalani@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20201029222738.482366-7-pmalani@chromium.org