CONFIG_ARCH_XGENE is not available for thedefaultarchitecture x86.
Result is shown for architecture arm64

AppliedMicro X-Gene SOC Family

configname: CONFIG_ARCH_XGENE

Linux Kernel Configuration
└─>Platform selection
└─>AppliedMicro X-Gene SOC Family
In linux kernel since version 3.11 (release Date: 2013-09-02)  
This enables support for AppliedMicro X-Gene SOC Family

is selected by
CONFIG_PHY_XGENE