CONFIG_ETRAX_NANDFLASH is not available for thedefaultarchitecture x86.
Result is shown for architecture cris

NAND flash support

modulename: nandflash.ko

configname: CONFIG_ETRAX_NANDFLASH

Linux Kernel Configuration
└─>NAND flash support
In linux kernel since version 2.6.13 (release Date: 2005-08-28)  
This option enables MTD mapping of NAND flash devices. Needed to use
NAND flash memories. If unsure, say Y.

source code:
arch/cris/arch-v32/drivers/mach-fs/nandflash.c