CONFIG_MACH_U8500 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

U8500 Development platform

modulename: board-mop500.ko

configname: CONFIG_MACH_U8500

Linux Kernel Configuration
└─>Ux500 target platform
└─>U8500 Development platform
In linux kernel since version 2.6.38 (release Date: 2011-03-14)  
Include support for the mop500 development platform.

source code: