* Update main.cpp
Add in TCXO_OPTIONAL variable for tcxoVoltage and a double-check for working in both modes.
* Update SX126xInterface.cpp
Make a change to the tcxoVoltage setting so that TCXO_OPTIONAL works if defined.
* Update variant.h
Added define for TCXO_OPTIONAL and the tcxoVoltage variable.
Added detail on the compatible boards.
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Co-authored-by: Ben Meadors <benmmeadors@gmail.com>