If Boseman wins a Golden Globe for his performance (he is nominated for best actor in a drama), some will believe it is out of sympathy. That thought should be dispelled now, as it diminishes his incredible work. In “Ma Rainey,” based on the like-titled August Wilson play, Boseman plays Levee Green, a trumpet player in a music world where black artists are mercilessly abused. Although capable of writing and playing with the best, Levee is relegated to backing Ma Rainey (Viola Davis, also nominated for a Globe), a black diva who has achieved enough fame and success to hold sway over white record producers.