configs: enable use of DT for all m68k boards

Enable DT usage for all m68k boards. To provide a
working single binary, the dts has been kept as embedded.

Signed-off-by: Angelo Dureghello <angelo@sysam.it>
diff --git a/configs/astro_mcf5373l_defconfig b/configs/astro_mcf5373l_defconfig
index 230c4cb..6d72bec 100644
--- a/configs/astro_mcf5373l_defconfig
+++ b/configs/astro_mcf5373l_defconfig
@@ -1,6 +1,7 @@
 CONFIG_M68K=y
 CONFIG_SYS_TEXT_BASE=0x00000000
 CONFIG_TARGET_ASTRO_MCF5373L=y
+CONFIG_DEFAULT_DEVICE_TREE="astro_mcf5373l"
 CONFIG_BOOTDELAY=1
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS=" console=ttyS2,115200 rootfstype=romfs loaderversion=$loaderversion"