platform/chrome: cros_ec_typec: Stash port driver info

Stash port number and a pointer to the driver-specific struct in the
local typec port struct.

These can be useful to the port driver to figure out how to communicate
with the Chrome EC when an altmode-driver related callback is invoked
from the Type-C class code.

Signed-off-by: Prashant Malani <pmalani@chromium.org>
Reviewed-by: Benson Leung <bleung@chromium.org>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20221228004648.793339-4-pmalani@chromium.org