ARM: software serial port integration (Tx only)

- be careful charging functionality not tested
- work corectly with baud rate 19200 and lover
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- TMR2 is used for Tx timing
- ADC for temp is disabled when Tx soft serial is active (maybe timing problem for other functionality)
- some logic are added for enable/disable some funcionality when eternal temp or Tx serial is active (probably not enough)
I think there is no sense to have HW & SW serial Tx in the same time.
As you suggested I introduced ENABLE_EXT_TEMP_AND_UART_COMMON_OUTPUT
and we can use it with existing ENABLE_SERIAL_LOG for activate/compile
correct module.
If we have one ARM directory for both version then probably it will be
necessary to have different namespace for TxSoftSerial & TxHwSerial, and
some additional logic in SerialLog.cpp to activate correct function from
TxSoftSerial or TxHwSerial module.