CONFIG_PPC_8xx is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

Freescale 8xx

modulename: m8xx_setup.ko

configname: CONFIG_PPC_8xx

Processor Type
└─>Freescale 8xx
In linux kernel since version 2.6.23 (release Date: 2007-10-09)  
source code:
arch/powerpc/platforms/8xx/m8xx_setup.c

is selected by
CONFIG_8xxx_WDT