usb: Update USB hub code to support super speed hubs

Super speed hubs (usb3 spec) have specific initialization
requirements.  Add the code necessary to detect and initialize these
hubs.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
Simplify README files - point to online documentation instead

The README file and README.CSM file have gotten a bit out of date.
Instead of maintaining technical information in the README file, point
new users to the SeaBIOS wiki.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>