greybus: connection: {en,dis}able fct flow in connection management

The AP must enable the FCT flow of APBA once it has received the response
from the AP that the connection between APBA and a module has been setted up.
Disable the flow of FCT tokens when destroying connections.

Signed-off-by: Fabien Parent <fparent@baylibre.com>
Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>