Espressif ESP8089 wireless SDIO devices

This node provides properties for controlling the ESP8089 wireless device.
The node is expected to be specified as a child node to the SDIO controller
that connects the device to the system.

Required properties:

 - compatible : Should be "esp,esp8089".

Optional properties:
 - esp,crystal-26M-en: Integer value for the crystal_26M_en firmware parameter

Example:

&mmc1 {
	#address-cells = <1>;
	#size-cells = <0>;

	vmmc-supply = <&reg_dldo1>;
	mmc-pwrseq = <&wifi_pwrseq>;
	bus-width = <4>;
	non-removable;
	status = "okay";

	esp8089: sdio_wifi@1 {
		compatible = "esp,esp8089";
		reg = <1>;
		esp,crystal-26M-en = <2>;
	};
};
