CONFIG_ARCH_MX5 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

i.MX50, i.MX51, i.MX53

configname: CONFIG_ARCH_MX5

Freescale CPU family:
└─>i.MX50, i.MX51, i.MX53
In linux kernel since version 2.6.34 (release Date: 2010-05-16)  
This enables support for machines using Freescale's i.MX50 and i.MX53
processors.