usb: gadget: Add variant of gether_setup to customize the device name

This is needed to avoid name collisions on SoCs that have both usb
gadget and usb host, where usb0 may be the rndis interface or a usb
ethernet adapter.

Signed-off-by: Mike Lockwood <lockwood@android.com>
Signed-off-by: Benoit Goby <benoit@android.com>