Digi Embedded Yocto 2.2-r2 for ConnectCore 6 and ConnectCore 6UL includes the NXP drivers for RS-485. They have not been tested by Digi on CC6UL.
You can try them on CC6UL following the CC6 instructions:
kernel 4.1:
https://github.com/digi-embedded/linux/blob/v4.1/dey-2.2/maint/Documentation/devicetree/bindings/serial/rs485.txt
https://www.digi.com/resources/documentation/digidocs/90001546/#reference/bsp/v4-1_cc6/r_universal_asynch_receiver_transmitter.htm
kernel 3.14:
https://www.digi.com/resources/documentation/digidocs/90001546/#reference/bsp/v3-14_cc6/r_universal_asynch_receiver_transmitter_v3-14.htm