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

Generic board-agnostic MIPS kernel


System type
└─>Generic board-agnostic MIPS kernel
In linux kernel since version 3.10 (release Date: 2013-06-30)  
Select this to build a kernel which aims to support multiple boards,
generally using a flattened device tree passed from the bootloader
using the boot protocol defined in the UHI (Unified Hosting
Interface) specification.