mediatek: mt7623: add explicit console= to U7623 kernel

The bootloader for legacy builds can't set it, so we end up unable to
log in on the serial port.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
(cherry picked from commit ea9ef8c9451a08aa4dbb6efcbe5f20d9b788ebd2)

target/linux/mediatek/patches-4.14/0227-arm-dts-Add-Unielec-U7623-DTS.patch

@@ -63,7 +63,7 @@ Subject: [PATCH] arm: dts: Add Unielec U7623 DTS
 +	};
 +
 +	chosen {
-+		bootargs = "root=/dev/mmcblk0p2 rootfstype=squashfs,f2fs";
++		bootargs = "root=/dev/mmcblk0p2 rootfstype=squashfs,f2fs console=ttyS0,115200";
 +		stdout-path = "serial2:115200n8";
 +	};
 +