CONFIG_ARCH_GEMINI is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Cortina Systems Gemini

configname: CONFIG_ARCH_GEMINI

Linux Kernel Configuration
└─>Cortina Systems Gemini
In linux kernel since version 2.6.30 (release Date: 2009-06-09)  
Support for the Cortina Systems Gemini family SoCs