Fix a typo resulted in USBD_SPEED_HS unregistering Full-Speed class
instead of High-Speed.

Signed-off-by: Tomasz Moń <tomasz.mon@nordicsemi.no>

Two main ideas behind setting maximum speed are:
  * Allow code and RAM optimizations at compile time
  * Allow High-Speed capable drivers to limit operating speed to user
    choice.

This commit only introduces the necessary Kconfig options but does not
implement any code or RAM optimizations and does not modify any driver.

Signed-off-by: Tomasz Moń <tomasz.mon@nordicsemi.no>

Allow compiler optimizations to remove High-Speed handling code. Knowing
that maximum operating speed is Full-Speed allows to reduce bulk buffers
from 512 to 64 bytes. More RAM optimizations are possible but this
commit only gets the low hanging fruits.

Signed-off-by: Tomasz Moń <tomasz.mon@nordicsemi.no>

Limit maximum operating speed in DCFG register if USB stack is
configured to support only Full-Speed.

Signed-off-by: Tomasz Moń <tomasz.mon@nordicsemi.no>

Introduce definitions to enable USB3 device controllers to be written.
The USB3 support got added to the core implementaiton, and to the Loopback
and CDC-ACM class only.

Signed-off-by: Josuah Demangeon <me@josuah.net>