arm/km: remove CONFIG_SYS_KWD_CONFIG from keymile-common.h

arm/km: remove CONFIG_SYS_KWD_CONFIG from keymile-common.h

This define is marvell specific, so it should be present in km_arm.
It is however not needed there either, since we set it to the default
value that is already set in include/asm/arch-kirkwood/config.h

Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
cc: Holger Brunck <holger.brunck@keymile.com>
cc: Prafulla Wadaskar <prafulla@marvell.com>
cc: Heiko Schocher <hs@denx.de>
cc: Wolfgang Denk <wd@denx.de>
cc: Detlev Zundel <dzu@denx.de>