As far as I know, experienced and heard 'bout offroading on trails in Turkey, there is no legal restriction to follow any track with your bike. There can be some prohibitions set by military or gendarme, especially at the South East Anatolia as Turkish Army is constantly performing operations at the region.
There can be offroad routes to recommend to you but it depends on which area you're to wander or will you make a Trans-Anatolia trip up to Iran border.
Regarding ''wild camping'', there is no obligation such as using camp sites. At the West of the country (Thrace, Aegean Area) you can easily and safely camp on any appropriate spot. On forest roads, especially at ''high-risk areas'' camping might be forbidden in order to prevent fires. Apart from these, it's safe, joyful camping at remote areas.
Last year, I made a 2-weeks trip to Gökçeada- the biggest island in TR), camped 95% of my time, nearlly at any spot I wished, made quite a bit of off-roading and was without any problems.
Good luck and enjoy!