CONFIG_SMP_ON_UP is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Allow booting SMP kernel on uniprocessor systems (EXPERIMENTAL)

configname: CONFIG_SMP_ON_UP

Linux Kernel Configuration
└─>Kernel Features
└─>Allow booting SMP kernel on uniprocessor systems (EXPERIMENTAL)
In linux kernel since version 2.6.37 (release Date: 2011-01-04)  
SMP kernels contain instructions which fail on non-SMP processors.
Enabling this option allows the kernel to modify itself to make
these instructions safe. Disabling it allows about 1K of space
savings.

If you don't know what to do here, say Y.