CONFIG_PLATFORM_WANT_DEFAULT_MEM is not available for thedefaultarchitecture x86.
Result is shown for architecture xtensa

CONFIG_PLATFORM_WANT_DEFAULT_MEM (not configurable)

configname: CONFIG_PLATFORM_WANT_DEFAULT_MEM

Linux Kernel Configuration
└─>Platform options
└─>PLATFORM_WANT_DEFAULT_MEM
In linux kernel since version 3.19 (release Date: 2015-02-08)