One piece of the Elvis Presley family tree has fallen into place. Per Variety, Maggie Gyllenhaal will be playing Gladys Presley, mother of the king of rock and roll, in the upcoming musical biopic Elvis from director Baz Luhrmann. Gyllenhaal joins the already cast Austin Butler as Elvis himself, and Tom Hanks as Colonel Tom Parker, Elvis' manager. [caption id="attachment_872939" align="alignright" width="350"] Image via Thomas R Machnitzki, CC[/caption] The Warner Bros. film, with a screenplay co-written by Luhrmann and regular collaborator Craig Pearce, will focus on Elvis' dramatic journey from poverty to superstardom. Along the …