CONFIG_ATARI is not available for thedefaultarchitecture x86.
Result is shown for architecture m68k

Atari support

configname: CONFIG_ATARI

Linux/68k Kernel Configuration
└─>Platform dependent setup
└─>Atari support
In linux kernel since version 2.6.12  
This option enables support for the 68000-based Atari series of
computers (including the TT, Falcon and Medusa). If you plan to use
this kernel on an Atari, say Y here and browse the material
available in Documentation/m68k; otherwise say N.