CONFIG_ARCH_MX1 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_ARCH_MX1 (not configurable)

configname: CONFIG_ARCH_MX1

Linux Kernel Configuration
└─>ARCH_MX1
In linux kernel since version 2.6.29 (release Date: 2009-03-23)  
is depended by
CONFIG_SOC_IMX1