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/crs328-4c-20s-4s-bit_defconfig b/configs/crs328-4c-20s-4s-bit_defconfig
index 513cc52..edfd0a4 100644
--- a/configs/crs328-4c-20s-4s-bit_defconfig
+++ b/configs/crs328-4c-20s-4s-bit_defconfig
@@ -1,6 +1,7 @@
 CONFIG_ARM=y
 CONFIG_ARCH_CPU_INIT=y
 CONFIG_ARCH_MVEBU=y
+CONFIG_SYS_KWD_CONFIG="board/mikrotik/crs3xx-98dx3236/kwbimage.cfg"
 CONFIG_SYS_TEXT_BASE=0x00800000
 CONFIG_SYS_MALLOC_F_LEN=0x2000
 CONFIG_TARGET_CRS3XX_98DX3236=y