CONFIG_ARCH_FPGA is not available for thedefaultarchitecture x86.
Result is shown for architecture unicore32
default or selected kernelversion does not have config value CONFIG_ARCH_FPGA.
Result is shown for kernelversion 6.9.9

CONFIG_ARCH_FPGA (not configurable)

configname: CONFIG_ARCH_FPGA

Linux Kernel Configuration
└─>System Type
└─>ARCH_FPGA
In linux kernel since version 2.6.39 (release Date: 2011-05-18)  
is selected by
CONFIG_PUV3_GPIO