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

Texas Instruments Keystone Devices

configname: CONFIG_ARCH_KEYSTONE

Linux Kernel Configuration
└─>Texas Instruments Keystone Devices
In linux kernel since version 3.10 (release Date: 2013-06-30)  
Support for boards based on the Texas Instruments Keystone family of
SoCs.



is selected by
CONFIG_TI_EDMA