SW: Upstream wpanusb

[jadonk]

https://elinux.org/BeagleBoard/GSoC/Ideas-2022#Upstream_wpanusb_and_bcfserial

These are the drivers that are used to enable Linux to use a BeagleConnect Freedom as a SubGHz IEEE802.15.4 radio (gateway). They need to be part of upstream Linux to simplify on-going support. There are several gaps that are known before they are acceptable upstream

Some notes from Stefan Schmidt:

1. The wpanusb linux driver is missing quite a few driver ops (listen before talk, set frame retries). I added rough sketches but these are non functional due to 2.
2. The zephyr firmware side needs to implement these ops as well and hook it up to the zephyr radio_api
3. A way to read the permanent extended address from the device to use in Linux is needed
4. The generic aspect of the firmware driver combo is missing completely. Band, supported channel, power levels, etc is all hard-coded in the linux driver and not queried from the device firmware. Its not even giving the page on which a channel is being set when changing it.
5. More driver ops are coming in right now as there is heavy work towards support management frames as well as active and passive scanning on the Linux stack. Which means these would need proper handling on the firmware side as well.