CONFIG_MACH_MX23EVK is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Support MX23EVK Platform

modulename: mach-mx23evk.ko

configname: CONFIG_MACH_MX23EVK

Linux Kernel Configuration
└─>Support MX23EVK Platform
In linux kernel since version 2.6.38 (release Date: 2011-03-14)  
Include support for MX23EVK platform. This includes specific
configurations for the board and its peripherals.

source code: