Hello @pb02,
You still can use the PINSEL, and do the process by yourself; nonetheless, there is functions as the one you point out, that helps you to do the process. It may be easier to do the configuration trough the functions, but it could be both ways according your needs.
For IOCON: I/O pin configuration, you can set a pinmux for a single pin with IOCONPinMuxSet() or set a pinmux for group of pins with IOCON_SetPinMuxing().

For further information related to the SDK and functions you could use for your configuration, please check the MCUXpresso SDK API Reference Manual: IOCON: I/O pin configuration.
Best regards, Raul.