As far as i know, you do not have to have a drive license for driving a motorbike at Chengdu. However, i’m not suggest a foreigner driving at Chengdu, because this is a new city to you , and there are tons of cars and motorbikes that you will be so mess up and confused. By the way, there are many taxis around every corner of this city and its very cheep.
Good luck! (Zhu ni hao yun!)