CONFIG_REDWOOD_6 is not available for thedefaultarchitecture x86.
Result is shown for architecture ppc

Redwood-6

modulename: redwood6.ko

and/or

ibmstbx25.ko

configname: CONFIG_REDWOOD_6

Machine Type
└─>Redwood-6
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
This option enables support for the IBM STBx25xx evaluation board.

source code:
arch/ppc/platforms/4xx/redwood6.c
is selected by
CONFIG_SMC91X