In ‘The Devil and Father Amorth,’ William Friedkin finds and films a real exorcist

There are no rotating heads or spewing green goop on display, but “Exorcist” director William Friedkin’s documentary, “The Devil and Father Amorth,” serves as a curious companion piece to his 1973 horror classic and has its own chilling, if limited, charms.

“At the time I made ‘The Exorcist,’ I…