ARM: ux500: Add node for the MMC GPIO regulator

There is a very simple mechanism to change and SDI's voltage which
consists of toggling some GPIOs. This scenario can be better handled
if we convert it to a GPIO regulator. This patch provides one which
can be read from Device Tree.
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

arch/arm/boot/dts/dbx5x0.dtsi

@@ -629,5 +629,19 @@ external-bus@50000000 {
 			ranges = <0 0x50000000 0x4000000>;
 			status = "disabled";
 		};
+
+		vmmci: regulator-gpio {
+			compatible = "regulator-gpio";
+
+			regulator-min-microvolt = <1800000>;
+			regulator-max-microvolt = <2600000>;
+			regulator-name = "mmci-reg";
+			regulator-type = "voltage";
+
+			gpios = <&tc3589x_gpio 18 0x4>;
+			gpio-enable = <&tc3589x_gpio 17 0x4>;
+			states = <1800000 0x1
+				  2900000 0x0>;
+		};
 	};
 };