serial: mxc: Add debug uart support

Add support for the debug UART to assist with early debugging.
Enable it for i.CoreM6 as an example.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index b7dd2ac..97cef7e 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -248,6 +248,14 @@
 	  will need to provide parameters to make this work. The driver will
 	  be available until the real driver model serial is running.
 
+config DEBUG_UART_MXC
+	bool "IMX Serial port"
+	depends on MXC_UART
+	help
+	  Select this to enable a debug UART using the serial_mxc driver. You
+	  will need to provide parameters to make this work. The driver will
+	  be available until the real driver model serial is running.
+
 config DEBUG_UART_UNIPHIER
 	bool "UniPhier on-chip UART"
 	depends on ARCH_UNIPHIER