km: clean up header files for KM Kirkwood boards

Remove unused preprocessor definitions and comments of already eliminated
code.

The Ethernet driver configuration is already declared in
arch/arm/mach-kirkwood/include/mach/config.h and, therefore, superfluous.

Signed-off-by: Pascal Linder <pascal.linder@edu.hefr.ch>
Signed-off-by: Holger Brunck <holger.brunck@ch.abb.com>
Signed-off-by: Stefan Roese <sr@denx.de>