serial: 8250_early: Add earlycon for BCM2835 aux uart

Define the OF early console for BCM2835 aux UART, which can be enabled
by passing "earlycon" on the boot command line. This UART is found on
BCM283x and BCM27xx SoCs, a.k.a. Raspberry Pi in its variants.
Signed-off-by: Matthias Brugger <mbrugger@suse.com>
Link: https://lore.kernel.org/r/20200126123314.3558-1-matthias.bgg@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_bcm2835aux.c

@@ -137,6 +137,24 @@ static struct platform_driver bcm2835aux_serial_driver = {
 };
 module_platform_driver(bcm2835aux_serial_driver);
 
+#ifdef CONFIG_SERIAL_8250_CONSOLE
+
+static int __init early_bcm2835aux_setup(struct earlycon_device *device,
+					const char *options)
+{
+	if (!device->port.membase)
+		return -ENODEV;
+
+	device->port.iotype = UPIO_MEM32;
+	device->port.regshift = 2;
+
+	return early_serial8250_setup(device, NULL);
+}
+
+OF_EARLYCON_DECLARE(bcm2835aux, "brcm,bcm2835-aux-uart",
+		    early_bcm2835aux_setup);
+#endif
+
 MODULE_DESCRIPTION("BCM2835 auxiliar UART driver");
 MODULE_AUTHOR("Martin Sperl <kernel@martin.sperl.org>");
 MODULE_LICENSE("GPL v2");