Add AU915 support

[mjunior-fitec]

Add AU915 band support, under CFG_au915

[ElectronicallyE]

@mjunior-fitec, thanks for writing up the support for AU915. Unfortunately, it's already been done in another pull request and it works without issue from my testing. Maybe, if you had suggestions, add them over there so everything is centralised and consistent?

Unfortunately, this library has not be updated for a while, so my bet would be to just use your pull request or the other one I linked as your primary one. :-(

[mjunior-fitec]

That's OK, thanks for answering.
Some 4 or 5 months ago I was looking for any implementation of the AU915 band LMIC and just couldn't find, so I wrote that changes. It would be great, since you already have some other - and well tested - solution, to make it public and searchable so anyone on this situation can take advantage of it.
Regards.

[matthijskooijman]

This repository is now deprecated. I'm grateful for your contribution, but it will no longer be merged. I'm recommending people to use the MCCI version of LMIC instead. If this PR addresses an issue that also exists in that version, I would encourage you to resubmit your contribution there, so it might benefit other users. I'm sorry for the inconvenience...