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

Freecom FSG-3

modulename: fsg-setup.ko

configname: CONFIG_MACH_FSG

Linux Kernel Configuration
└─>Intel IXP4xx Implementation Options
└─>Freecom FSG-3
In linux kernel since version 2.6.27 (release Date: 2008-10-09)  
Say 'Y' here if you want your kernel to support Freecom's
FSG-3 device. For more information on this platform,
see http://www.nslu2-linux.org/wiki/FSG3/HomePage

source code:
selects
CONFIG_PCI