CONFIG_NIOS2_KERNEL_REGION_BASE_BOOL is not available for thedefaultarchitecture x86.
Result is shown for architecture nios2

Set custom kernel region base address


Linux Kernel Configuration
└─>Advanced setup
└─>Set custom kernel region base address
In linux kernel since version 3.19 (release Date: 2015-02-08)  
This option allows you to set the virtual address of the kernel region.

Say N here unless you know what you are doing.