exynos: Add debug UART support for Samsung S5P serial

Add a debug UART implementation for this serial driver. It does not set up
pinmux automatically - this must be done before calling debug_uart_init().

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index b5a91b7..fd126a8 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -53,6 +53,13 @@
 	  U-Boot when running on top of EFI (Extensive Firmware Interface).
 	  This is a type of BIOS used by PCs.
 
+config DEBUG_UART_S5P
+	bool "Samsung S5P"
+	help
+	  Select this to enable a debug UART using the serial_s5p driver. You
+	  will need to provide parameters to make this work. The driver will
+	  be available until the real driver-model serial is running.
+
 endchoice
 
 config DEBUG_UART_BASE