Convert CONFIG_SYS_KWD_CONFIG to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_KWD_CONFIG

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/kmnusa_defconfig b/configs/kmnusa_defconfig
index 06b2d1f..3696572 100644
--- a/configs/kmnusa_defconfig
+++ b/configs/kmnusa_defconfig
@@ -3,6 +3,7 @@
 CONFIG_SYS_DCACHE_OFF=y
 CONFIG_ARCH_CPU_INIT=y
 CONFIG_ARCH_KIRKWOOD=y
+CONFIG_SYS_KWD_CONFIG="board/keymile/km_arm/kwbimage_128M16_1.cfg"
 CONFIG_SYS_TEXT_BASE=0x07d00000
 CONFIG_TARGET_KM_KIRKWOOD=y
 CONFIG_KM_FPGA_CONFIG=y