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/ds109_defconfig b/configs/ds109_defconfig
index ba74ece..8e2aea9 100644
--- a/configs/ds109_defconfig
+++ b/configs/ds109_defconfig
@@ -8,6 +8,7 @@
 CONFIG_INITRD_TAG=y
 CONFIG_STATIC_MACH_TYPE=y
 CONFIG_MACH_TYPE=527
+CONFIG_SYS_KWD_CONFIG="board/Synology/ds109/kwbimage.cfg"
 CONFIG_SYS_TEXT_BASE=0x600000
 CONFIG_NR_DRAM_BANKS=2
 CONFIG_TARGET_DS109=y