Revert "usb: gadget: allow to enable legacy drivers without USB_ETH"

Romain Izard reported the following about commit 7a9618a22aad:

As it reached Linus' tree with v4.15-rc3, I recently noticed the following commit that triggered a Kconfig request. I believe that this change does not make sense.

7a9618a22aa usb: gadget: allow to enable legacy drivers without USB_ETH

USB_ETH was not a dependency, but a default value for the choice. As the choice was marked as "optional", it was possible to remove this value when building.

After this modification, the Kconfig choice option does not contain anything anymore, so it is useless. It is also possible to select multiple built-in legacy drivers. This builds, but will not work as expected as only one legacy driver can be bound to an USB device controller at a time.

Hence revert commit 7a9618a22aad.

Signed-off-by Bart Van Assche <[email protected]>

Cc Romain Izard <[email protected]>

Cc Arnd Bergmann <[email protected]>

Cc Stephen Rothwell <[email protected]>

Cc Masahiro Yamada <[email protected]>

Cc Hannes Reinecke <[email protected]>

Cc Nicholas Bellinger <[email protected]>

Cc Andrzej Pietrasiewicz <[email protected]>

Cc [email protected]

Cc Felipe Balbi <[email protected]>