powerpc/km82xx: fix compile issue for mgcoge2ne

commit 91a3c14c (ppc, mgcoge: add DIP switch detection)
introduces an compile error due to an missing define in the
mgcoge2ne.h. DIP switch detection is valid for both boards.

Signed-off-by: Holger Brunck <holger.brunck@keymile.com>
cc: Wolfgang Denk <wd@denx.de>
cc: Heiko Schocher <hs@denx.de>