CONFIG_MACH_MT7623 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

MediaTek MT7623 SoCs support

configname: CONFIG_MACH_MT7623

Linux Kernel Configuration
└─>Mediatek MT65xx & MT81xx SoC
└─>MediaTek MT7623 SoCs support
In linux kernel since version 3.10 (release Date: 2013-06-30)