Usb net gadget changes

Remove the USB Gadget Composite CDC ACM/ECM interfaces from the
Linux build in favor of the USB Ethernet Gadget.  Enable the USB
Ethernet Gadget's support of RNDIS and CDC EEM.  Windows platforms
support RNDIS natively while Linux can use either RNDIS or EEM
(preferring EEM on modern systems).

Correct the inittab and barebox parameters accordingly.