platform/chrome: cros_ec_typec: Support DP alt mode

Handle Chrome EC mux events to configure on-board muxes correctly while
entering DP alternate mode. Since we don't surface SVID and VDO
information regarding the DP alternate mode, configure the Type C
muxes directly from the port driver. Later, when mode discovery
information is correctly surfaced to the driver, we can register the DP
alternate mode driver and let it handle the mux configuration.

Also, modify the struct_typec_state state management to account for the
addition of DP alternate mode.

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>