Get Rpmsg character devices running

Hi @stefan_e.tx

@hfranco.tx sent this to me a while ago: https://community.toradex.com/t/rpmsg-character-device-driver-in-torizon-core-6-2/19464/5?u=gerko

I did it with the original code from the MCUXpresso SDK … pingpong examples and with the slightly modified code from this thread: https://community.toradex.com/t/rpmsg-char-driver-not-sending-data-on-imx8mm/18466