serial: imx: Support common rs485 binding for RTS polarity

Invoke the ->rs485_config callback on probe to adjust the initial RTS
polarity based on the UART's device properties.

This implicitly fixes a bug:  If RTS control is not available, rs485
should be disabled even if it was enabled through a device property.
Log an error when that occurs.

Cc: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/imx.c

@@ -2092,6 +2092,12 @@ static int serial_imx_probe(struct platform_device *pdev)
 
 	uart_get_rs485_mode(&pdev->dev, &sport->port.rs485);
 
+	if (sport->port.rs485.flags & SER_RS485_ENABLED &&
+	    (!sport->have_rtscts || !sport->have_rtsgpio))
+		dev_err(&pdev->dev, "no RTS control, disabling rs485\n");
+
+	imx_rs485_config(&sport->port, &sport->port.rs485);
+
 	/* Disable interrupts before requesting them */
 	reg = readl_relaxed(sport->port.membase + UCR1);
 	reg &= ~(UCR1_ADEN | UCR1_TRDYEN | UCR1_IDEN | UCR1_RRDYEN |