USB 2 connection to USB 3
You simply only connect the D-, D+, and GND lines, and leave the SS lines open (I literally did this quite recently, using the exact same HUB IC from TI). See below comparing the two:



Hope this helps. Also, you'll find that USB 3.0/3.1 is 9 pins, not 5 as you said (VBUS, D-, D+, SSTX-, SSTX+, GND, SSRX-, SSRX+, and GND).