CONFIG_ARCH_K3 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm64

Texas Instruments Inc. K3 multicore SoC architecture

configname: CONFIG_ARCH_K3

Linux Kernel Configuration
└─>Platform selection
└─>Texas Instruments Inc. K3 multicore SoC architecture
In linux kernel since version 3.10 (release Date: 2013-06-30)  
This enables support for Texas Instruments' K3 multicore SoC
architecture.