CONFIG_ARCH_MXC is not available for the selected architecture x86.
Result is shown for architecture arm

Freescale i.MX family

modulename: soc-imx.ko

configname: CONFIG_ARCH_MXC

Linux Kernel Configuration
└─>Freescale i.MX family
In linux kernel since version 2.6.23 (release Date: 2007-10-09)
Support for Freescale MXC/iMX-based family of processors
source code:
drivers/soc/imx/soc-imx.c