arm64: dts: hikey960: add WL1837 Bluetooth device node

This adds the serial slave device for the WL1837 Bluetooth interface.
Signed-off-by: Guodong Xu <guodong.xu@linaro.org>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>

arch/arm64/boot/dts/hisilicon/hi3660-hikey960.dts

@@ -9,6 +9,7 @@
 
 #include "hi3660.dtsi"
 #include "hikey960-pinctrl.dtsi"
+#include <dt-bindings/gpio/gpio.h>
 
 / {
 	model = "HiKey960";
@@ -63,6 +64,16 @@ &uart3 {
 	status = "okay";
 };
 
+&uart4 {
+	status = "okay";
+
+	bluetooth {
+		compatible = "ti,wl1837-st";
+		enable-gpios = <&gpio15 6 GPIO_ACTIVE_HIGH>;
+		max-speed = <921600>;
+	};
+};
+
 &uart6 {
 	/* On Low speed expansion */
 	label = "LS-UART1";