A power plant involving a BP joint venture would be built near the town of Tupman, Calif. Photo: Will EvansThe federal government is giving a joint venture involving oil giant BP millions of dollars in stimulus money to build a power plant on farmland near the tiny Kern County town of Tupman, Calif., even as the company faces heavy government pressure and a criminal probe into the Gulf of Mexico oil spill. BP is benefiting from a $308 million federal grant over several years for the cutting-edge power plant on cotton and alfalfa fields seven miles from the western edge …