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

Marvell Armada XP boards

configname: CONFIG_MACH_ARMADA_XP

Linux Kernel Configuration
└─>Marvell Engineering Business Unit (MVEBU) SoCs
└─>Marvell Armada XP boards
In linux kernel since version 3.1 (release Date: 2011-10-24)  
Say 'Y' here if you want your kernel to support boards based
on the Marvell Armada XP SoC with device tree.