USB Gadget device support

[Maccraft123]

C100PA and C201PA both have OTG available for user,
so it shouldn't be that hard to use g_ether and plug it into OpenWRT router or other PC and use it as gateway.
Warning: M-M USB cables have 5v shorted on both ends, so it has to be disconnected before use or it will fry one or two ends
It requires DT changes.

Relevant links:
https://www.linuxsecrets.com/elinux-wiki/images/8/81/Useful_USB_Gadgets_on_Linux.pdf
https://wiki.postmarketos.org/wiki/USB_Internet
https://elixir.bootlin.com/linux/latest/source/drivers/usb/dwc2
raspberrypi/linux#1212 (comment)