ARM: dts: imx6ull-colibri: enable UHS-I for USDHC1

Allows to use the SD interface at a higher speed mode if the card
supports it. For this the signaling voltage is switched from 3.3V to
1.8V under the usdhc1's drivers control.

Signed-off-by: Igor Opaniuk <igor.opaniuk@toradex.com>
Reviewed-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
diff --git a/arch/arm/boot/dts/imx6ul.dtsi b/arch/arm/boot/dts/imx6ul.dtsi
index fc388b8..91a0ced 100644
--- a/arch/arm/boot/dts/imx6ul.dtsi
+++ b/arch/arm/boot/dts/imx6ul.dtsi
@@ -857,6 +857,8 @@
 					 <&clks IMX6UL_CLK_USDHC1>,
 					 <&clks IMX6UL_CLK_USDHC1>;
 				clock-names = "ipg", "ahb", "per";
+				fsl,tuning-step= <2>;
+				fsl,tuning-start-tap = <20>;
 				bus-width = <4>;
 				status = "disabled";
 			};
@@ -870,6 +872,8 @@
 					 <&clks IMX6UL_CLK_USDHC2>;
 				clock-names = "ipg", "ahb", "per";
 				bus-width = <4>;
+				fsl,tuning-step= <2>;
+				fsl,tuning-start-tap = <20>;
 				status = "disabled";
 			};