arm64: dts: imx8mm-nitrogen-r2: rework USDHC1

Add VMMC and VQMMC description for USDHC1 (eMMC).
There are comming directly from the alimentation
stage, so add the vref_3V3 fixed regulator.
Signed-off-by: Adrien Grassein <adrien.grassein@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mm-nitrogen-r2.dts

@@ -17,6 +17,13 @@ reg_vref_1v8: regulator-vref-1v8 {
 		regulator-max-microvolt = <1800000>;
 	};
 
+	reg_vref_3v3: regulator-vref-3v3 {
+		compatible = "regulator-fixed";
+		regulator-name = "vref-3v3";
+		regulator-min-microvolt = <3300000>;
+		regulator-max-microvolt = <3300000>;
+	};
+
 	reg_wlan_vmmc: regulator-wlan-vmmc {
 		compatible = "regulator-fixed";
 		pinctrl-names = "default";
@@ -209,6 +216,8 @@ &usdhc1 {
 	pinctrl-0 = <&pinctrl_usdhc1>;
 	pinctrl-1 = <&pinctrl_usdhc1_100mhz>;
 	pinctrl-2 = <&pinctrl_usdhc1_200mhz>;
+	vmmc-supply = <&reg_vref_3v3>;
+	vqmmc-supply = <&reg_vref_1v8>;
 	status = "okay";
 };