Hello,
Please note that the i.MX SDK is not supported by the MCUXpresso IDE, this include the config tools included in the IDE, with the exception of the i.MX RT, the toolchains supported are IAR and GCC ARM only.
We have support for pin configuration and DDR tools only, all other needed changes should be done manually.
Finally, inside the SDK package you'll find example for both RPMSG communication as well as for UART for the Cortex-M.
Best regards,
Aldo.