km/common: remove unused code

The 82xx board mgcoge3ne was removed from the codebase, so this is dead
code.

Signed-off-by: Holger Brunck <holger.brunck@keymile.com>
Cc: Heiko Schocher <hs@denx.de>
Reviewed-by: Heiko Schocher <hs@denx.de>