ui: usbselector: refactor USB Speed rendering, add USB 3.1

ui: usbselector: refactor USB Speed rendering, add USB 3.1

Fixes also an issue where unregonized (often faster) devices would
get recognized as "USB 1.x" due to the else fallback.

Now, if we do not recognize the speed value, just print the speed
with the MBps unit (it's not exactly megabit per second, but mega
baud (= symbols) per second - the effective rate is dependent on the
used signal encoding)

adapt widths a bit further

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>