Audi is planning an entry-level turbocharged R8, slotting a more affordable version of the supercar in beneath the current V10 models. The existing 2017 R8 - which we tested on the road and on the track recently - is powered by a naturally-aspirated 5.2-liter V10 good for as much as 610 HP and 398 lb-ft of torque, but the V8 …