CONFIG_MACH_ARMADILLO5X0 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Support Atmark Armadillo-500 Development Base Board

modulename: armadillo5x0.ko

and/or

mach-armadillo5x0.ko

configname: CONFIG_MACH_ARMADILLO5X0

Linux Kernel Configuration
└─>Support Atmark Armadillo-500 Development Base Board
In linux kernel since version 2.6.31 (release Date: 2009-09-09)  
Include support for Atmark Armadillo-500 platform. This includes
specific configurations for the board and its peripherals.

source code:
arch/arm/mach-mx3/armadillo5x0.c