arm: s5p4418: dm_serial: remove old code / add DEBUG_UART

Remove init of UART-clock and UART-reset in arch_cpu_init(). Add DEBUG_UART
to s5p4418_nanopi2_defconfig.

Signed-off-by: Stefan Bosch <stefan_b@posteo.net>
diff --git a/include/configs/s5p4418_nanopi2.h b/include/configs/s5p4418_nanopi2.h
index 2fa44e6..fec1bfd 100644
--- a/include/configs/s5p4418_nanopi2.h
+++ b/include/configs/s5p4418_nanopi2.h
@@ -76,11 +76,9 @@
 /*-----------------------------------------------------------------------
  * serial console configuration
  */
-#define CFG_PL011_CLOCK		50000000
-#define CFG_PL01x_PORTS		{(void *)PHY_BASEADDR_UART0, \
-					 (void *)PHY_BASEADDR_UART1, \
-					 (void *)PHY_BASEADDR_UART2, \
-					 (void *)PHY_BASEADDR_UART3}
+
+/* 150MHz is the clock rate set by SPL (uart0) */
+#define CFG_PL011_CLOCK		150000000
 
 /*-----------------------------------------------------------------------
  * BACKLIGHT