CONFIG_MACH_MX31LITE is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
default or selected kernelversion does not have config value CONFIG_MACH_MX31LITE.
Result is shown for kernelversion 6.9.9

Support MX31 LITEKIT (LogicPD)

modulename: mach-mx31lite.ko

configname: CONFIG_MACH_MX31LITE

Linux Kernel Configuration
└─>Freescale i.MX family
└─>Support MX31 LITEKIT (LogicPD)
In linux kernel since version 2.6.27 (release Date: 2008-10-09)  
Include support for MX31 LITEKIT platform. This includes specific
configurations for the board and its peripherals.

source code:
/arch/arm/mach-imx/