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

Mapped kernel support

configname: CONFIG_MAPPED_KERNEL

Linux Kernel Configuration
└─>Mapped kernel support
In linux kernel since version 2.6.12  
Change the way a Linux kernel is loaded into memory on a MIPS64
machine. This is required in order to support text replication on
NUMA. If you need to understand it, read the source code.

depends
CONFIG_SGI_IP27

is depended by
CONFIG_REPLICATE_KTEXT