Hi
NAND Flash is serial Flash and so can not be addresses linearly by the processor (it needs a SW layer between it to map its memory blocks and manage bad blocks etc.).
Code in NAND Flash is normally loaded to the processor's RAM and executed from there.
It is possible to run program from external parallel Flash or (SD)RAM connected to the FlexBus. Typically to run large code the code is copied from NAND Flash to SDRAM and executed there.
Regards
Mark