NEW YORK — AT&T’s $48.5 billion purchase of DirecTV is set to close after winning clearance from the Federal Communications Commission. The Justice Department had already cleared the deal, which will create the largest provider of cable or satellite TV in the U.S., with 26.4 million cable and satellite TV subscribers. That’s more than Comcast as well as a bigger Charter, which is seeking government approval to buy Time Warner Cable. Suppliers of TV are buying one another as video from Internet competitors like Netflix gets more popular and costs rise for channels. Adding TV customers gives AT&T more power to negotiate with big media companies over prices for those channels. The deal also combines a nationwide satellite TV service with a nationwide wireless network as time spent on mobile devices increases.