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

VIA/WonderMedia 85xx

modulename: vt8500.ko

and/or

clk-vt8500.ko

and/or

irq-vt8500.ko

and/or

irq.ko

configname: CONFIG_ARCH_VT8500

Linux Kernel Configuration
└─>VIA/WonderMedia 85xx
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/

is selected by
CONFIG_FB_WM8505