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

Gumstix Overo board

modulename: board-overo.ko

configname: CONFIG_MACH_OVERO

Linux Kernel Configuration
└─>TI OMAP/AM/DM/DRA Family
└─>TI OMAP2/3/4 Specific Features
└─>Gumstix Overo board
In linux kernel since version 2.6.28 (release Date: 2008-12-24)  
source code:
arch/arm/mach-omap2/board-overo.c