usb: device_next: Change speed selection Kconfig dependency

In my opinion, the user is supposed to configure the speed of the stack
and drivers ough to honor that choice. However current Zephyr USB
maintainer imposes that the dependency is the other way round, i.e.
that user first needs to disable High-Speed chirp at driver level and
only then can select Full-Speed only operation. Adhere to the
arbitrarily set up rule to allow this really necessary functionality to
enter Zephyr.

I consider this change to be harmful because it opens up a Kconfig trap
that allows configuring High-Speed capable stack with a device driver
limited to Full-Speed only operation.

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