CONFIG_MACH_MX28EVK is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Support MX28EVK Platform

modulename: mach-mx28evk.ko

configname: CONFIG_MACH_MX28EVK

Linux Kernel Configuration
└─>Support MX28EVK Platform
In linux kernel since version 2.6.38 (release Date: 2011-03-14)  
Include support for MX28EVK platform. This includes specific
configurations for the board and its peripherals.

source code:
arch/arm/mach-mxs/mach-mx28evk.c

depends
CONFIG_ARCH_MXS