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

Cavium Inc. Thunder SoC Family

configname: CONFIG_ARCH_THUNDER

Linux Kernel Configuration
└─>Platform selection
└─>Cavium Inc. Thunder SoC Family
In linux kernel since version 3.10 (release Date: 2013-06-30)  
This enables support for Cavium's Thunder Family of SoCs.