EXCLUSIVE: The woman who teamed with Marvin Gaye on a string of 1960s Motown hits before dying of a brain tumor at age 24 is getting her own biopic. Tammi Terrell will be played by The Vampire Diaries star Kat Graham, who also is working her debut album with producer Babyface. Maryam Myika Day wrote the untitled project, which marks Graham’s feature debut and is being produced by Robert Teitel, Rose Ganguzza and Hilary Shor. Shooting is set for next year. The film follows…