CONFIG_MACH_MOP500 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

U8500 Development platform, MOP500 versions

modulename: board-mop500.ko

and/or

board-mop500-audio.ko

configname: CONFIG_MACH_MOP500

Linux Kernel Configuration
└─>Ux500 target platform (boards)
└─>U8500 Development platform, MOP500 versions
In linux kernel since version 3.1 (release Date: 2011-10-24)  
Include support for the MOP500 development platform.

source code:
/arch/arm/mach-ux500/


is selected by
CONFIG_MACH_UX500_DT