CONFIG_ARCH_R8A7791 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

R-Car M2 (R8A77910)

modulename: setup-r8a7791.ko

and/or

clock-r8a7791.ko

and/or

clk-rcar-gen2.ko

configname: CONFIG_ARCH_R8A7791

Linux Kernel Configuration
└─>R-Car M2 (R8A77910)
In linux kernel since version 3.10 (release Date: 2013-06-30)  
source code:
/arch/arm/mach-shmobile/