CONFIG_ARCH_IMX is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
default or selected kernelversion does not have config value CONFIG_ARCH_IMX.
Result is shown for kernelversion 5.4.123

IMX

configname: CONFIG_ARCH_IMX

ARM system type
└─>IMX
In linux kernel since version 2.6.12  
is selected by
CONFIG_CPU_ARM920T