CONFIG_ARCH_R8A7794 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

R-Car E2 (R8A77940)

modulename: setup-r8a7794.ko

and/or

clk-rcar-gen2.ko

configname: CONFIG_ARCH_R8A7794

Linux Kernel Configuration
└─>Renesas ARM SoCs
└─>R-Car E2 (R8A77940)
In linux kernel since version 3.10 (release Date: 2013-06-30)  
source code:
arch/arm/mach-shmobile/setup-r8a7794.c