tty: serial/8250: remove console dependency for mediatek

If the mediatek serial port driver is built-in, but serial
console is disabled in Kconfig (e.g. when the serial driver
itself is a loadable module), we get this build error:

drivers/built-in.o: In function `early_mtk8250_setup':
undefined reference to `early_serial8250_setup'

To avoid that problem, this patch encloses the early_mtk8250_setup
function in #ifdef CONFIG_SERIAL_8250_CONSOLE, the same symbol
that guards the early_serial8250_setup function.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Eddie Huang <eddie.huang@mediatek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_mtk.c

@@ -305,6 +305,7 @@ static struct platform_driver mtk8250_platform_driver = {
 };
 module_platform_driver(mtk8250_platform_driver);
 
+#ifdef CONFIG_SERIAL_8250_CONSOLE
 static int __init early_mtk8250_setup(struct earlycon_device *device,
 					const char *options)
 {
@@ -317,6 +318,7 @@ static int __init early_mtk8250_setup(struct earlycon_device *device,
 }
 
 OF_EARLYCON_DECLARE(mtk8250, "mediatek,mt6577-uart", early_mtk8250_setup);
+#endif
 
 MODULE_AUTHOR("Matthias Brugger");
 MODULE_LICENSE("GPL");