CONFIG_ARCH_SIFIVE is not available for the selected architecture x86.
Result is shown for architecture riscv or 64BIT
SiFive SoCs
configname: CONFIG_ARCH_SIFIVE
Linux Kernel Configuration
└─>SoC selection
└─>SiFive SoCs
In linux kernel since version 4.14.326 (release Date: 2023-09-23)
This enables support for SiFive SoC platform hardware.