arm: ls1021atwr: Convert to driver model and enable serial support

Convert ls1021atwr_nor to driver model support. As a start, enable
ns16550 serial port driver.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/include/configs/ls1021atwr.h b/include/configs/ls1021atwr.h
index c12ba3a..bbef2a7 100644
--- a/include/configs/ls1021atwr.h
+++ b/include/configs/ls1021atwr.h
@@ -271,7 +271,9 @@
 #else
 #define CONFIG_CONS_INDEX		1
 #define CONFIG_SYS_NS16550_SERIAL
+#ifndef CONFIG_DM_SERIAL
 #define CONFIG_SYS_NS16550_REG_SIZE	1
+#endif
 #define CONFIG_SYS_NS16550_CLK		get_serial_clock()
 #endif