serial: imx: add earlycon support

Earlycon allows to have an early debugging console that doesn't need
to be statically configured in the kernel config, like earlyprintk,
but is set up through the stdout-path DT property.

This allows to have the early debugging always built into the
kernel and enabled on demand without clashing between different boards
or architectures.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/Kconfig

@@ -582,6 +582,7 @@ config SERIAL_IMX_CONSOLE
 	bool "Console on IMX serial port"
 	depends on SERIAL_IMX=y
 	select SERIAL_CORE_CONSOLE
+	select SERIAL_EARLYCON if OF
 	help
 	  If you have enabled the serial port on the Freescale IMX
 	  CPU you can make it the console by answering Y to this option.