serial: imx: Enable RTSD only when needed

Currently, this IRQ is always enabled. Some devices might mux these pins
to other I/Os, like I2C. This could lead to spurious interrupts.

This commit makes this IRQ optional, by using the field have_rtscts.
Signed-off-by: Nandor Han <nandor.han@ge.com>
Signed-off-by: Romain Perier <romain.perier@collabora.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/imx.c

@@ -1299,7 +1299,9 @@ static int imx_startup(struct uart_port *port)
 		imx_enable_dma(sport);
 
 	temp = readl(sport->port.membase + UCR1);
-	temp |= UCR1_RRDYEN | UCR1_RTSDEN | UCR1_UARTEN;
+	temp |= UCR1_RRDYEN | UCR1_UARTEN;
+	if (sport->have_rtscts)
+			temp |= UCR1_RTSDEN;
 
 	writel(temp, sport->port.membase + UCR1);