CONFIG_M548x is not available for thedefaultarchitecture x86.
Result is shown for architecture m68k

MCF548x

configname: CONFIG_M548x

CPU
└─>MCF548x
In linux kernel since version 2.6.37 (release Date: 2011-01-04)  
Freescale ColdFire 5480/5481/5482/5483/5484/5485 processor support.