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

CONFIG_XILINX_VIRTEX (not configurable)

modulename: xilinx_intc.ko

configname: CONFIG_XILINX_VIRTEX

Linux Kernel Configuration
└─>XILINX_VIRTEX
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
source code:

is selected by
CONFIG_SPI_XILINX