CONFIG_XILINX_ML403 is not available for thedefaultarchitecture x86.
Result is shown for architecture ppc

Xilinx-ML403

modulename: xilinx_ml403.ko

configname: CONFIG_XILINX_ML403

Machine Type
└─>Xilinx-ML403
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
This option enables support for the Xilinx ML403 evaluation board.

source code:
arch/ppc/platforms/4xx/xilinx_ml403.c