CONFIG_FPU is not available for thedefaultarchitecture x86.
Result is shown for architecture openrisc

FPU support

modulename: fpu.ko

and/or

kernel_mode_fpu.ko

configname: CONFIG_FPU

Linux Kernel Configuration
└─>Processor type and features
└─>FPU support
In linux kernel since version 2.6.12  
Say N here if you want to disable all floating-point related procedures
in the kernel and reduce binary size.

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

source code:
arch/riscv/kernel/
is selected by
CONFIG_RISCV_ISA_V