CONFIG_ATH79 is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

Atheros AR71XX/AR724X/AR913X based boards

configname: CONFIG_ATH79

System type
└─>Atheros AR71XX/AR724X/AR913X based boards
In linux kernel since version 2.6.38 (release Date: 2011-03-14)  
Support for the Atheros AR71XX/AR724X/AR913X SoCs.


is selected by
CONFIG_AG71XX