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

Rockchip Platforms

modulename: rockchip.ko

configname: CONFIG_ARCH_ROCKCHIP

Linux Kernel Configuration
└─>Platform selection
└─>Rockchip Platforms
In linux kernel since version 3.10 (release Date: 2013-06-30)  
This enables support for the ARMv8 based Rockchip chipsets,
like the RK3368.