CONFIG_UNCACHED_MAPPING is not available for thedefaultarchitecture x86.
Result is shown for architecture sh

CONFIG_UNCACHED_MAPPING (not configurable)

modulename: uncached.ko

configname: CONFIG_UNCACHED_MAPPING

Linux Kernel Configuration
└─>Memory management options
└─>UNCACHED_MAPPING
In linux kernel since version 2.6.34 (release Date: 2010-05-16)  
source code:
arch/sh/mm/uncached.c