CONFIG_NTB_AMD is not available for thedefaultarchitecture x86.
Result is shown for architecture 64BIT

AMD Non-Transparent Bridge support

modulename: ntb_hw_amd.ko

configname: CONFIG_NTB_AMD

Linux Kernel Configuration
└─>Device Drivers
└─>Non-Transparent Bridge support
└─>AMD Non-Transparent Bridge support
In linux kernel since version 4.1 (release Date: 2015-06-21)  
This driver supports AMD NTB on capable Zeppelin hardware.

If unsure, say N.

source code:
drivers/ntb/hw/amd/ntb_hw_amd.c