CONFIG_MACH_MIC256 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
default or selected kernelversion does not have config value CONFIG_MACH_MIC256.
Result is shown for kernelversion 6.9.9

Omicron MIC256

modulename: omixp-setup.ko

configname: CONFIG_MACH_MIC256

Linux Kernel Configuration
└─>Intel IXP4xx Implementation Options
└─>Omicron MIC256
In linux kernel since version 3.1 (release Date: 2011-10-24)  
Say 'Y' here if you want your kernel to support the MIC256
board from OMICRON electronics GmbH.

source code: