CONFIG_ARCH_MX2 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

MX2-based

modulename: iomux-mx1-mx2.ko

configname: CONFIG_ARCH_MX2

MXC/iMX Base Type
└─>MX2-based
In linux kernel since version 2.6.27 (release Date: 2008-10-09)  
This enables support for systems based on the Freescale i.MX2 family

source code:
is selected by
CONFIG_CPU_ARM926T