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

Build big-endian kernel

configname: CONFIG_CPU_BIG_ENDIAN

Linux Kernel Configuration
└─>Build big-endian kernel
In linux kernel since version 2.6.12  
Say Y if you plan on running a kernel in big-endian mode.
Note that your board must be properly built and your board
port must properly enable any big-endian related features
of your chipset/board/processor.