Add bluetooth node to uart4.

--- a/arch/arm/boot/dts/nxp/imx/imx6qdl-sr-som-brcm.dtsi
+++ b/arch/arm/boot/dts/nxp/imx/imx6qdl-sr-som-brcm.dtsi
@@ -128,6 +127,10 @@
 	pinctrl-0 = <&pinctrl_microsom_brcm_bt &pinctrl_microsom_uart4>;
 	uart-has-rtscts;
 	status = "okay";
+
+	bluetooth {
+		compatible = "brcm,bcm4330-bt";
+	};
 };
 
 /* USDHC1 - Connected to optional BRCM Wifi/BT/FM */
