CONFIG_PPC_MEM_KEYS is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

PowerPC Memory Protection Keys

modulename: pkeys.ko

configname: CONFIG_PPC_MEM_KEYS

Linux Kernel Configuration
└─>Kernel options
└─>PowerPC Memory Protection Keys
In linux kernel since version 4.2 (release Date: 2015-08-30)  
Memory Protection Keys provides a mechanism for enforcing
page-based protections, but without requiring modification of the
page tables when an application changes protection domains.

For details, see
source code:
arch/powerpc/mm/pkeys.c