arm: s5p4418: dm_serial: add driver source code

Add dm_serial driver source code for S5P4418 SOC. Extend the "arm,pl011"
driver by init of UART-clock and UART-reset.

Signed-off-by: Stefan Bosch <stefan_b@posteo.net>
diff --git a/MAINTAINERS b/MAINTAINERS
index 3fc4cd0..5f9636f 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -436,6 +436,7 @@
 F:	drivers/i2c/nx_i2c.c
 F:	drivers/mmc/nexell_dw_mmc_dm.c
 F:	drivers/pinctrl/nexell/
+F:	drivers/serial/serial_s5p4418_pl011.c
 F:	drivers/video/nexell/
 F:	drivers/video/nexell_display.c
 F:	include/configs/s5p4418_nanopi2.h