CONFIG_ETRAX_NANDBOOT is not available for thedefaultarchitecture x86.
Result is shown for architecture cris
default or selected kernelversion does not have config value CONFIG_ETRAX_NANDBOOT.
Result is shown for kernelversion 6.7-rc3

Boot from NAND flash


Linux Kernel Configuration
└─>Boot from NAND flash
In linux kernel since version 2.6.25 (release Date: 2008-04-16)  
This options enables booting from NAND flash devices.
Say Y if your boot code, kernel and root file system is in
NAND flash. Say N if they are in NOR flash.