arm64: dts: imx8mp-verdin: add 88W8997 serdev to uart4

Use the serdev feature to load the driver for the 88W8997 bluetooth
driver.
Signed-off-by: Stefan Eichenberger <stefan.eichenberger@toradex.com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mp-verdin-wifi.dtsi

@@ -65,6 +65,11 @@ &uart4 {
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_bt_uart>;
 	status = "okay";
+
+	bluetooth {
+		compatible = "mrvl,88w8997";
+		max-speed = <921600>;
+	};
 };
 
 /* On-module Wi-Fi */