CONFIG_MACH_MESON8 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Amlogic Meson8 SoCs support

configname: CONFIG_MACH_MESON8

Linux Kernel Configuration
└─>Amlogic Meson SoCs
└─>Amlogic Meson8 SoCs support
In linux kernel since version 3.19 (release Date: 2015-02-08)