arm64: dts: qcom: sdm845-oneplus-common: enable debug UART

A labelled diagram showing the location of the Rx and Tx testpoints for
the OnePlus 6 is available on the postmarketOS wiki:

https://wiki.postmarketos.org/wiki/Serial_debugging:Cable_schematics

The device uses 1.8v UART at a baud rate of 115200, bootloader output is
also available here.
Signed-off-by: Caleb Connolly <caleb@connolly.tech>
Link: https://lore.kernel.org/r/20210720153125.43389-3-caleb@connolly.techSigned-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

arch/arm64/boot/dts/qcom/sdm845-oneplus-common.dtsi

@@ -19,9 +19,14 @@
 
 / {
 	aliases {
+		serial0 = &uart9;
 		hsuart0 = &uart6;
 	};
 
+	chosen {
+		stdout-path = "serial0:115200n8";
+	};
+
 	gpio-keys {
 		compatible = "gpio-keys";
 		label = "Volume keys";
@@ -526,6 +531,11 @@ bluetooth {
 	};
 };
 
+&uart9 {
+	label = "LS-UART1";
+	status = "okay";
+};
+
 &ufs_mem_hc {
 	status = "okay";