Most Gravel routes in Norway have sections that are only for bikes, and thus it will be impossible to follow the bike on every track/road. A lot of gravel roads are also Toll meaning an extra fee is paid at a barrier to access them.

This is a good mix-surface route that is good to cycle and drive. The mountain road closes in late September
http://www.ridewithgps.com/routes/39610649?privacy_code=4CzR8m4I9Of4CpOo

This is a long cycling route that offers both gravel and paved sections. It can be driven for most of the route.
http://www.cyclenorway.com/routes/national-cycle-routes/overview/route-9/the-wilderness-route/

Tour de Dovre: this has some section where you can drive and other where you must drive the main road while the cyclists rides a gravel path next to it.
http://www.ridewithgps.com/routes/39611333?privacy_code=xazexPNZobuJfiwv

Mjølkevegen: For most of this, you can drive, but once again, expect some small sections for cyclists only where the car will have follow the paved road instead.
http://www.ridewithgps.com/routes/39601999?privacy_code=LGrMqtGBNEh7jDe7
http://www.cyclenorway.com/routes/national-cycle-routes/overview/route-5/middelalderdalen-mjolkevegen/

This is also a good route from Oslo. The first part is on paved roads but has many kilometers of gravel the further east you head. Once you reach the town of Rena, the final part to Lillehammer is unsuitable for vehicles.
http://www.ridewithgps.com/routes/43372579