CONFIG_WALNUT is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc
default or selected kernelversion does not have config value CONFIG_WALNUT.
Result is shown for kernelversion 6.8.2

Walnut

modulename: walnut.ko

configname: CONFIG_WALNUT

Linux Kernel Configuration
└─>Walnut
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
This option enables support for the IBM PPC405GP evaluation board.

source code: