LMN: code readability and performance improvements TODOs

[elsalahy]

A number of code improvements can be done to make the LoRa MAC Node code better in regards to performance and readability.

Here are the TODOs:
for hal_LoraMacNode.c:

• Todo: Implement general purpose LMN hal init
• Todo: Fix constant slave addressing -> Done
• Todo: Fix warnings-> Done

for atecc608a-tnglora-se.c:

• Todo: clean up this file before PR, add more checks for status
• Todo: add status checks for atca calls
• Todo: add SE derivation for multicast keys
• Todo: handle dev and join-euis readings from SE slots -> Done
• Todo: use the secure element random generators

[elsalahy]

For src/boards/SAMR34/sx1276-board.c:
Todo: handle low power by controlling TCXO and rfswitch_pin

[johanstokking]

It's not our job to tidy LMN and it will make merging updates an unnecessarily painful process.

Please scope this issue to non-LMN code.

[elsalahy]

Yeah Ok I understand your point and it's my target to avoid doing any unnecessary changes to LMN.
We are on an agreement on this.

You will see in the Fork, I only do changes to SAMR34 (as we are the ones who added the support)
and TNGLoRa