Hi. I too just downgraded a Toshiba Satellite S855D-S5120 from Windows 8.1 to Windows 7 Pro. Same missing USB 3.0 and memory card reader as others. Toshiba website official USB 3.0 filter driver is a no go so I googled "AMD USB 3.0 hub and host controller" and got a Lenovo support site as first result. I tried it and it has a newer AMD USB 3.0 driver for the Trinity chipset that works.
http://support.lenovo.com/us/en/downloads/ds036687
For the "usb 2.0-crw", that is indeed the memory card driver and Realtek has it here:
http://www.realtek.com/downloads/downloadsView.aspx?Langid=3&PNid=15&PFid=25&Level=4&Conn=3&DownTypeID=3&GetDown=false
Now for the 3rd and final driver, SM BUS Controller, again I googled "AMD SMB BUS controller" and got the Lenovo support site and that driver worked too so go here:
http://support.lenovo.com/us/en/downloads/ds019868
Toshiba is definitely behind in the driver support department. At least Lenovo drivers work and that's what counts. Thanks Jarotech for the heads up on the CRW being the USB digital card reader and that it's a Realtek IC.