CONFIG_CUSTOM_CACHE_SETTINGS is not available for thedefaultarchitecture x86.
Result is shown for architecture nios2

Custom cache settings

configname: CONFIG_CUSTOM_CACHE_SETTINGS

Linux Kernel Configuration
└─>Platform options
└─>Custom cache settings
In linux kernel since version 3.19 (release Date: 2015-02-08)  
This option allows you to tweak the cache settings used during early
boot (where the information from device tree is not yet available).
There should be no reason to change these values. Linux will work
perfectly fine, even if the Nios II is configured with smaller caches.

Say N here unless you know what you are doing.