CONFIG_SMP_UP is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

CONFIG_SMP_UP (not configurable)

modulename: smp-up.ko

configname: CONFIG_SMP_UP

Linux Kernel Configuration
└─>Kernel type
└─>SMP_UP
In linux kernel since version 2.6.25 (release Date: 2008-04-16)  
source code:
is depended by
CONFIG_MIPS_MT_SMP