By Bernardo VizcainoApril 24 (Reuters) - Pakistani conglomerate Engro CorpEGCH.KA , a former unit of Exxon Mobil Corp XOM.N , plans to raise as much as 4 billion rupees ($40.9 million) through listed sukuk (Islamic bonds), Pakistan Credit Rating Agency Limited said.The proposed sukuk would be secured and offered in two tenors: a three-year 3 billion rupee tranche with a 13 percent profit rate, and