serial-arc: switch to DM

Now when all infrastructure in ARC is ready for it let's switch ARC UART
to driver model.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Simon Glass <sjg@chromium.org>
diff --git a/configs/arcangel4-be_defconfig b/configs/arcangel4-be_defconfig
index 990c74a..36ea6be 100644
--- a/configs/arcangel4-be_defconfig
+++ b/configs/arcangel4-be_defconfig
@@ -1,5 +1,10 @@
 CONFIG_ARC=y
 CONFIG_CPU_BIG_ENDIAN=y
 CONFIG_TARGET_ARCANGEL4=y
+CONFIG_DM=y
+CONFIG_DM_SERIAL=y
+CONFIG_DEFAULT_DEVICE_TREE="arcangel4"
 CONFIG_SYS_TEXT_BASE=0x81000000
 CONFIG_SYS_CLK_FREQ=70000000
+CONFIG_OF_CONTROL=y
+CONFIG_OF_EMBED=y