CONFIG_M53xx is not available for thedefaultarchitecture x86.
Result is shown for architecture m68k

CONFIG_M53xx (not configurable)

modulename: m53xx.ko

configname: CONFIG_M53xx

Linux Kernel Configuration
└─>M53xx
In linux kernel since version 3.1 (release Date: 2011-10-24)  
source code:
arch/m68k/coldfire/
depends
CONFIG_COLDFIRE

is depended by
CONFIG_M537x