ARM: dts: pi400: Force stdout-path to serial0

The upstream Pi DTS files select serial1 for stdout-path, but because of
the way the downstream kernel numbers UARTS, serial0 is required in the
downstream DTS. Using the wrong value breaks U-boot.

In the 6.6 kernel the downstream Pi 400 DTS was made closer to upstream,
inheriting most of its content from the Pi 4B DTS, but because of the
order of inclusion it lost the override for stdout-path. Restore that
override.

See: raspberrypi/firmware#1875
Signed-off-by: Phil Elwell <phil@raspberrypi.com>

arch/arm/boot/dts/broadcom/bcm2711-rpi-400.dts

@@ -43,6 +43,12 @@
 // =============================================
 // Downstream rpi- changes
 
+/ {
+	chosen {
+		stdout-path = "serial0:115200n8";
+	};
+};
+
 &audio_pins {
 	brcm,pins = <>;
 	brcm,function = <>;