CONFIG_X86_SMP is not available for thedefaultarchitecture x86.
Result is shown for architecture i386
default or selected kernelversion does not have config value CONFIG_X86_SMP.
Result is shown for kernelversion 5.4.123

CONFIG_X86_SMP (not configurable)

modulename: smp.ko

configname: CONFIG_X86_SMP

Linux Kernel Configuration
└─>X86_SMP
In linux kernel since version 2.6.12  
source code:
arch/i386/kernel/