platform/chrome: cros_ec_typec: Rename discovery struct

Rename the sop_disc data struct which is used to store PD discovery data
to the more generic name of disc_data. It can then be re-used to store
and process cable discovery data.

Signed-off-by: Prashant Malani <pmalani@chromium.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Benson Leung <bleung@chromium.org>
Link: https://lore.kernel.org/r/20201116201150.2919178-7-pmalani@chromium.org