CONFIG_MACH_MX51_3DS is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
default or selected kernelversion does not have config value CONFIG_MACH_MX51_3DS.
Result is shown for kernelversion 6.2.5

Support MX51PDK (3DS)

modulename: board-mx51_3ds.ko

configname: CONFIG_MACH_MX51_3DS

Linux Kernel Configuration
└─>Support MX51PDK (3DS)
In linux kernel since version 2.6.36 (release Date: 2010-10-20)  
Include support for MX51PDK (3DS) platform. This includes specific
configurations for the board and its peripherals.

source code:
arch/arm/mach-mx5/board-mx51_3ds.c