CONFIG_ARCH_SIFIVE is not available for thedefaultarchitecture x86.
Result is shown for architecture riscv

CONFIG_ARCH_SIFIVE (not configurable)

configname: CONFIG_ARCH_SIFIVE

Linux Kernel Configuration
└─>SoC selection
└─>ARCH_SIFIVE
In linux kernel since version 4.14.326 (release Date: 2023-09-23)  
is selected by
CONFIG_PCIE_FU740