CONFIG_MIPS_ATLAS is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

Support for MIPS Atlas board

modulename: fixup-atlas.ko

configname: CONFIG_MIPS_ATLAS

Linux/MIPS Kernel Configuration
└─>Machine selection
└─>Support for MIPS Atlas board
In linux kernel since version 2.6.12  
This enables support for the QED R5231-based MIPS Atlas evaluation
board.

source code:
arch/mips/pci/fixup-atlas.c