serial: imx: Only wakeup via RTSDEN bit if the system has RTS/CTS

The wakeup mechanism via RTSDEN bit relies on the system using the RTS/CTS
lines, so only allow such wakeup method when the system actually has
RTS/CTS support.

Fixes: bc85734b126f ("serial: imx: allow waking up on RTSD")
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Martin Kaiser <martin@kaiser.cx>
Acked-by: Fugang Duan <fugang.duan@nxp.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/imx.c

@@ -2225,12 +2225,14 @@ static void serial_imx_enable_wakeup(struct imx_port *sport, bool on)
 		val &= ~UCR3_AWAKEN;
 	writel(val, sport->port.membase + UCR3);
 
-	val = readl(sport->port.membase + UCR1);
-	if (on)
-		val |= UCR1_RTSDEN;
-	else
-		val &= ~UCR1_RTSDEN;
-	writel(val, sport->port.membase + UCR1);
+	if (sport->have_rtscts) {
+		val = readl(sport->port.membase + UCR1);
+		if (on)
+			val |= UCR1_RTSDEN;
+		else
+			val &= ~UCR1_RTSDEN;
+		writel(val, sport->port.membase + UCR1);
+	}
 }
 
 static int imx_serial_port_suspend_noirq(struct device *dev)