CONFIG_PPC_MPC837x is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

CONFIG_PPC_MPC837x (not configurable)

configname: CONFIG_PPC_MPC837x

Linux Kernel Configuration
└─>PPC_MPC837x
In linux kernel since version 2.6.25 (release Date: 2008-04-16)  

is selected by
CONFIG_GPIO_MPC8XXX