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

Cortina Systems Gemini

configname: CONFIG_ARCH_GEMINI

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


depends
 or CONFIG_ARCH_MULTI_V4

is selected by
CONFIG_CRYPTO_DEV_SL3516