CONFIG_MACH_EM_X270 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CompuLab EM-x270 platform

modulename: em-x270.ko

configname: CONFIG_MACH_EM_X270

Select target board
└─>CompuLab EM-x270 platform
In linux kernel since version 2.6.23 (release Date: 2007-10-09)  
source code:
arch/arm/mach-pxa/em-x270.c
selects
CONFIG_PXA27x