CONFIG_ARCH_MX503 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
default or selected kernelversion does not have config value CONFIG_ARCH_MX503.
Result is shown for kernelversion 6.2.5

i.MX50 + i.MX53

configname: CONFIG_ARCH_MX503

Freescale CPU family:
└─>i.MX50 + i.MX53
In linux kernel since version 3 (release Date: 2011-07-21)  
This enables support for machines using Freescale's i.MX50 and i.MX51