Pretty sure mine has one one line running down the tunnel then a Tee thats on the chassis below the tunnel exit which goes to both rear calipers, so I would say its a single system ? 1 litre should be enough to fully purge and bleed the system I would have thought.
The key is the master cylinder--if there are two hard line connections to it then you have a dual breaking system (which is highly likely in any modern car)
