Universal Music label boss Antonio “L.A.” Reid is hip-hopping to TV. The chairman of Universal’s Island Def Jam will leave to become a judge on Simon Cowell’s upcoming Fox TV show “The X-Factor,” according to people familiar with discussions. News Corp. owns Fox and The Post. Reid, who has been angling for an exit from Universal for months in order to pursue other interests, got his wish this week when the show’s producers made him a firm offer. Universal agreed to let Reid out of his contract, which expires at the end of the year.