As it prepares to merge with BB&T, Atlanta-based SunTrust Banks will double its investment in the Atlanta community each year over the next three years.“It has been $50 million for the last three years,” said Bill Rogers, SunTrust’s chairman and CEO, in an extensive interview on Tuesday. “We are going to double that amount. It will be  $100 million a year for next three years for a total of $300 million.”