MILAN, March 31 (Reuters) - Fiat's CEO has flown to Chrysler LLC's [CBS.UL] home town of Detroit to meet trade unions and creditors after U.S. authorities gave the carmakers 30 days to set up a partnership to save Chrysler. Sergio Marchionne flew late on Monday to Detroit after U.S. President Barack Obama ordered Chrysler to accelerate its efforts to survive and prepare itself for possible bankruptcy. Marchionne was accompanied by Alfredo Altavilla, Fiat's head of business development, who is