CONFIG_ATH25 is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

Atheros AR231x/AR531x SoC support

configname: CONFIG_ATH25

System type
└─>Atheros AR231x/AR531x SoC support
In linux kernel since version 3.19 (release Date: 2015-02-08)  
Support for Atheros AR231x and Atheros AR531x based boards