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

Realtek Platforms

configname: CONFIG_ARCH_REALTEK

Linux Kernel Configuration
└─>Platform selection
└─>Realtek Platforms
In linux kernel since version 3.10 (release Date: 2013-06-30)  
This enables support for the ARMv8 based Realtek chipsets,
like the RTD1295.