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/M52277EVB_stmicro_defconfig b/configs/M52277EVB_stmicro_defconfig
index cafc861..84733f6 100644
--- a/configs/M52277EVB_stmicro_defconfig
+++ b/configs/M52277EVB_stmicro_defconfig
@@ -1,6 +1,7 @@
 CONFIG_M68K=y
 CONFIG_SYS_TEXT_BASE=0x43E00000
 CONFIG_TARGET_M52277EVB=y
+CONFIG_DEFAULT_DEVICE_TREE="M52277EVB_stmicro"
 CONFIG_SYS_EXTRA_OPTIONS="CF_SBF,SYS_STMICRO_BOOT"
 CONFIG_BOOTDELAY=3
 # CONFIG_DISPLAY_BOARDINFO is not set