platform/chrome: cros_typec_vdm: Add Attention support

Add support to retrieve VDM attention messages and forward them to the
appropriate alt mode driver.

Signed-off-by: Prashant Malani <pmalani@chromium.org>
Reviewed-by: Benson Leung <bleung@chromium.org>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20230126205620.3714994-2-pmalani@chromium.org