CONFIG_ARCH_VT8500 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_ARCH_VT8500 (not configurable)

modulename: irq.ko

and/or

clk-vt8500.ko

configname: CONFIG_ARCH_VT8500

Linux Kernel Configuration
└─>ARCH_VT8500
In linux kernel since version 2.6.39 (release Date: 2011-05-18)  
Support for VIA/WonderMedia VT8500/WM85xx System-on-Chip.

source code:
/arch/arm/mach-vt8500/