CONFIG_MACH_MX51_BABBAGE is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Support MX51 BABBAGE platforms

modulename: mach-mx51_babbage.ko

and/or

board-mx51_babbage.ko

configname: CONFIG_MACH_MX51_BABBAGE

Linux Kernel Configuration
└─>Support MX51 BABBAGE platforms
In linux kernel since version 2.6.34 (release Date: 2010-05-16)  
Include support for MX51 Babbage platform, also known as MX51EVK in
u-boot. This includes specific configurations for the board and its
peripherals.

source code:
arch/arm/mach-mx5/board-mx51_babbage.c