CONFIG_XILINX_VIRTEX_5_FXT is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

CONFIG_XILINX_VIRTEX_5_FXT (not configurable)

modulename: virtex.ko

configname: CONFIG_XILINX_VIRTEX_5_FXT

Linux Kernel Configuration
└─>XILINX_VIRTEX_5_FXT
In linux kernel since version 2.6.27 (release Date: 2008-10-09)  
source code:
arch/powerpc/platforms/44x/virtex.c