Add Semtech SX1272 support. Add basic LoRaWAN node and gateway support

[andresmanelli]

Content

• Arch definitions for Semtech's SX1272/3 PHY
• "high" level APIs to access the variables (some of them distributed across register boundaries)
• protocol.lora definitions
• protocol.semtech_udp_forwarder (used in LoRaWAN gateway)
• radio-sx1272 applet, that sends / receives packages using LoRa modulation, PHY to PHY
• radio-lora applet, that provides node and gateway functionality for LoRaWAN protocol.

Raw PHY Tx can and LoRaWAN node is connected to a socket for data transmission.

I tested both use cases with two Glasgow boards, and a TheThingsNetwork application with good results.

What is implemented in LoRaWAN

• Network join via OTAA (Session keys computed and stored)
• Message encryption / decryption per specification
• Receive windows, with different RF parameters
• DLsettings.RX2DataRate use for configuring the proper RF parameters in 2nd receive window

Caveats

• Somehow the gateway receive socket takes more and more time to get the downlink packet, and I couldn't figure out why..

TODO

There is plenty TODO on the RF regions, MAC commands, Frequency hopping, ... but I won't do that in the near future so I though of submitting this PR as-is (functional, but somehow incomplete in a specification point of view)

Let me know the required changes to meet the project style/guidelines. I tried to follow other applets/arch code style.

Thanks!

[whitequark]

Thanks for the PR! At a very quick glance, code looks reasonable. I'm currently very busy with nMigen, so it will take a significant amount of time for me to properly review and merge your PR.