serial: fsl_lpuart: Remove the alias node dependence

Numbering the ttyLPn space should not depend on the generic name
"serial<n>".

If don't add the alias node like:"serial0 = &lpuart0;", then lpuart
will probe failed:
[    0.773410] fsl-lpuart 2950000.serial: failed to get alias id, errno -19

So remove the alias node dependence, and add the support for allocate the
line port automatically.
Signed-off-by: Yuan Yao <yao.yuan@nxp.com>
Signed-off-by: Vabhav Sharma <vabhav.sharma@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/fsl_lpuart.c

@@ -232,6 +232,8 @@
 /* IMX lpuart has four extra unused regs located at the beginning */
 #define IMX_REG_OFF	0x10
 
+static DEFINE_IDA(fsl_lpuart_ida);
+
 struct lpuart_port {
 	struct uart_port	port;
 	struct clk		*clk;
@@ -2143,9 +2145,12 @@ static int lpuart_probe(struct platform_device *pdev)
 
 	ret = of_alias_get_id(np, "serial");
 	if (ret < 0) {
-		dev_err(&pdev->dev, "failed to get alias id, errno %d\n", ret);
+		ret = ida_simple_get(&fsl_lpuart_ida, 0, UART_NR, GFP_KERNEL);
+		if (ret < 0) {
+			dev_err(&pdev->dev, "port line is full, add device failed\n");
 			return ret;
 		}
+	}
 	if (ret >= ARRAY_SIZE(lpuart_ports)) {
 		dev_err(&pdev->dev, "serial%d out of range\n", ret);
 		return -EINVAL;
@@ -2246,6 +2251,8 @@ static int lpuart_remove(struct platform_device *pdev)
 
 	uart_remove_one_port(&lpuart_reg, &sport->port);
 
+	ida_simple_remove(&fsl_lpuart_ida, sport->port.line);
+
 	clk_disable_unprepare(sport->clk);
 
 	if (sport->dma_tx_chan)
@@ -2384,6 +2391,7 @@ static int __init lpuart_serial_init(void)
 
 static void __exit lpuart_serial_exit(void)
 {
+	ida_destroy(&fsl_lpuart_ida);
 	platform_driver_unregister(&lpuart_driver);
 	uart_unregister_driver(&lpuart_reg);
 }