CONFIG_MPC83xx is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

83xx Board Type

configname: CONFIG_MPC83xx

Linux Kernel Configuration
└─>83xx Board Type
In linux kernel since version 2.6.25 (release Date: 2008-04-16)  

depends
CONFIG_PPC_83xx

is selected by
CONFIG_MPC837x_RDB