To see if it's the turbo, take the outlet pipe off the compressor housing and if the seals have gone you'll see oil (varying from small streaks to a liberal coating everywhere depending on how bad it is) in the housing and the outlet pipe.

To see if the rings have had it you usually do compression test, record the readimgs, pour a tablespoonful of oil down the spark plug holes, repeat the compression test and if the compression readings are substantially higher then the rings are shot.