CONFIG_MPC831x_RDB is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc
Freescale MPC831x RDB
modulename: mpc831x_rdb.ko
configname: CONFIG_MPC831x_RDB
Linux Kernel Configuration
└─>83xx-based boards
└─>Freescale MPC831x RDB
In linux kernel since version 2.6.25 (release Date: 2008-04-16)
This option enables support for the MPC8313 RDB and MPC8315 RDB boards.