platform/chrome: cros_ec_typec: Make disc_done flag partner-only

Change the disc_done flag, which indicates whether PD discovery is
complete, to sop_disc_done instead, since we will process SOP and SOP'
discovery data separately.

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/20201116201150.2919178-5-pmalani@chromium.org