Garchomp is fast. Not to mention airborne. Tyranitar, however, even without shooting beams from it's mouth, is pretty literally a mountain. If Garchomp can make a dent in the rocky armor, a collection of swift bites and hits could end Tyranitar. However, given Tyranitar's armor, it could just sit there and Garchomp would be too tired before piercing the armor.
If it's an aggressive Tyranitar, i suppose Garchomp could tire it with it's superior agility and ability to take to the air, Tyranitar could get tired chasing Garchomp and Garchomp could hack at Tyranitar so that if it DOES wake up during the battle, it would be much too sore to move much. It's a question of how smart both pokemon are, i suppose. If either is smarter, they'd win this battle. Armor vs. Speed becomes a game of wits pretty easy if i'm correct.