CONFIG_MPC85xx_RDB is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc
Freescale MPC85xx RDB
modulename: mpc85xx_rdb.ko
configname: CONFIG_MPC85xx_RDB
Linux Kernel Configuration
└─>Freescale Book-E Machine Type
└─>Freescale MPC85xx RDB
In linux kernel since version 2.6.32 (release Date: 2009-12-02)
This option enables support for the MPC85xx RDB (P2020 RDB) board