txs02612 SDIO switch

If a txs02612 SDIO switch (and level shifter) is connected
to a sdio/mmc port of a SoC we have effectively two interfaces
as a result. The switch is controlled by a GPIO.

Required properties:

	compatible = “ti,txs02612”

	select-gpio:	the channel select gpio.

	ports:	two new mmc ports. For details check with
		Documentation//devicetree/bindings/mmc/mmc.txt

Optional properties:

	mmc:	phandle to reference the sdio/mmc port of the SoC.
		If the node is a subnode of the mmc port of the SoC
		this phandle can be omitted.

Example:

	mmc-expander {
		compatible = “ti,txs02612”;
		mmc = <&mmc1>;
		select-gpio = <&gpio3 18 0>;	/* gpio3_82 */
		ports {
			eMMC: port@0 {
				reg = <0>;
				bus-width: 8;
				bus-width = <8>;
				non-removable;
			};
			uSD: port@1 {
				reg = <1>;
				bus-width: 4;
				cd-gpios = <&gpio3 13 GPIO_ACTIVE_LOW>;	/* gpio3_77 */
				wp-gpios = <&gpio3 15 GPIO_ACTIVE_HIGH>;	/* gpio3_79 */
			};
	};
