ok, no problem, then in this case please go to the kernel code:
linux/arm/configs/ to get inspired from the evk board.
Then, keep in mind that all 5 UARTs are not available all at the same time. AUART0_CTS/RTS cannot be configured with AUART4_RX/TX.
When selected in your config files, the IOMUX will be automatically correctly selected when compiling.
Check arch/arm/mach-mx28/serial.c