A board can optionaly define RC_SERIAL_SWAP_USING_SINGLEWIRE
If the board is wired board with TX to the input (Swapped) and
the SoC does not support U[S]ART level RX-TX swapping to allow
useing onewire to do the swap if and only if:
RC_SERIAL_SWAP_USING_SINGLEWIRE is defined
RC_SERIAL_SWAP_RXTX is defined
TIOCSSWAP is defined and retuns !OK
TIOCSSINGLEWIRE is defined