ARM: dts: imx6: add mmdc ipg clock

i.MX6 SoCs has MMDC clock gates in CCM CCGR, add
clock property for MMDC driver's clock operation.
Signed-off-by: NAnson Huang <Anson.Huang@nxp.com>
Signed-off-by: NShawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6qdl.dtsi

@@ -1115,6 +1115,7 @@
 			mmdc0: mmdc@21b0000 { /* MMDC0 */
 				compatible = "fsl,imx6q-mmdc";
 				reg = <0x021b0000 0x4000>;
+				clocks = <&clks IMX6QDL_CLK_MMDC_P0_IPG>;
 			};
 
 			mmdc1: mmdc@21b4000 { /* MMDC1 */

arch/arm/boot/dts/imx6sl.dtsi

@@ -921,6 +921,7 @@
 			mmdc: mmdc@21b0000 {
 				compatible = "fsl,imx6sl-mmdc", "fsl,imx6q-mmdc";
 				reg = <0x021b0000 0x4000>;
+				clocks = <&clks IMX6SL_CLK_MMDC_P0_IPG>;
 			};
 
 			rngb: rngb@21b4000 {

arch/arm/boot/dts/imx6sll.dtsi

@@ -770,6 +770,7 @@
 			mmdc: memory-controller@21b0000 {
 				compatible = "fsl,imx6sll-mmdc", "fsl,imx6q-mmdc";
 				reg = <0x021b0000 0x4000>;
+				clocks = <&clks IMX6SLL_CLK_MMDC_P0_IPG>;
 			};
 
 			ocotp: ocotp-ctrl@21bc000 {

arch/arm/boot/dts/imx6sx.dtsi

@@ -1002,6 +1002,7 @@
 			mmdc: mmdc@21b0000 {
 				compatible = "fsl,imx6sx-mmdc", "fsl,imx6q-mmdc";
 				reg = <0x021b0000 0x4000>;
+				clocks = <&clks IMX6SX_CLK_MMDC_P0_IPG>;
 			};
 
 			fec2: ethernet@21b4000 {

arch/arm/boot/dts/imx6ul.dtsi

@@ -917,6 +917,7 @@
 			mmdc: mmdc@21b0000 {
 				compatible = "fsl,imx6ul-mmdc", "fsl,imx6q-mmdc";
 				reg = <0x021b0000 0x4000>;
+				clocks = <&clks IMX6UL_CLK_MMDC_P0_IPG>;
 			};
 
 			weim: weim@21b8000 {