[loggers] Direct memory logger

Direct memory logger using flash memory.
Yes, for that you would currently need to use macros (similar to GpsLink or InsLink).
But if you know it's a UART, don't use the macros, use the functions...

Also you normally don't need to explicitly initialize the uart, that is automatically done in mcu_init with ` PERIPHERALS_AUTO_INIT` and if `USE_UARTx` is true.