General Motors (GM) and Chrysler are to get additional loans and more time from the US treasury as the troubled carmakers work on plans to try and make themselves viable and stave off bankruptcy.   GM could get as much as $5 billion more in federal loans, while Chrysler could get $500 million as they race against government-imposed deadlines to restructure, according to a government report filed Tuesday.  A special inspector general on the auto industry and bank bailout programs says the money will be made available for working capital.