tty: serial: imx: disable irq after suspend

If any key on console is pressed when board is suspended,
board hangs.

Driver's interrupt handler must be guaranteed not to run while
resume/suspend_noirq() are being executed. See include/linux/pm.h
for details.

Tested on i.MX6 based board.

The idea of this fix is based on commit in official i.MX kernel tree:
http://git.freescale.com/git/cgit.cgi/imx/linux-2.6-imx.git
commit 81e8e7d91d81 ("tty: serial: imx: disable irq after suspend")

Disable rx irq after suspend to avoid interrupt coming in early resume.
Signed-off-by: Fugang Duan <B38611@freescale.com>
Signed-off-by: Maxim Yu. Osipov <mosipov@ilbers.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/imx.c

@@ -2321,6 +2321,7 @@ static int imx_serial_port_suspend(struct device *dev)
 	serial_imx_enable_wakeup(sport, true);
 
 	uart_suspend_port(&imx_reg, &sport->port);
+	disable_irq(sport->port.irq);
 
 	/* Needed to enable clock in suspend_noirq */
 	return clk_prepare(sport->clk_ipg);
@@ -2335,6 +2336,7 @@ static int imx_serial_port_resume(struct device *dev)
 	serial_imx_enable_wakeup(sport, false);
 
 	uart_resume_port(&imx_reg, &sport->port);
+	enable_irq(sport->port.irq);
 
 	clk_unprepare(sport->clk_ipg);