talmud gemara - Who established the Shema?

The Gemara in Berachos 12b says "They sought to establish [various passages] in the Shema" and "they establish[ed] the passage of tzitzis in the Shema" (Artscroll trans.)

I had thought that the obligation to recite the Shema was biblical. Who established the passage of tzitzis in the Shema, and if only this passage was established - with Shema and V'haya being biblical requirements - does this make Vayomer derabanan?