CONFIG_CELL_CPU is not available for the selected architecture x86.
Result is shown for architecture powerpc

Cell Broadband Engine

configname: CONFIG_CELL_CPU

CPU selection
└─>Cell Broadband Engine
In linux kernel since version 3.1 (release Date: 2011-10-24)

depends
CONFIG_PPC_BOOK3S_64
NOT CONFIG_CC_IS_CLANG
NOT CONFIG_CPU_LITTLE_ENDIAN