ARM: dts: imx: make MMDC node name generic

Node name should be generic, so use "memory-controller"
instead of "mmdc" for MMDC node name, also remove "mmdc"
label for platforms with single MMDC node.
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6qdl.dtsi

@@ -1138,13 +1138,13 @@ romcp@21ac000 {
 				reg = <0x021ac000 0x4000>;
 			};
 
-			mmdc0: mmdc@21b0000 { /* MMDC0 */
+			mmdc0: memory-controller@21b0000 { /* MMDC0 */
 				compatible = "fsl,imx6q-mmdc";
 				reg = <0x021b0000 0x4000>;
 				clocks = <&clks IMX6QDL_CLK_MMDC_P0_IPG>;
 			};
 
-			mmdc1: mmdc@21b4000 { /* MMDC1 */
+			mmdc1: memory-controller@21b4000 { /* MMDC1 */
 				reg = <0x021b4000 0x4000>;
 			};
 

arch/arm/boot/dts/imx6sl.dtsi

@@ -922,7 +922,7 @@ i2c3: i2c@21a8000 {
 				status = "disabled";
 			};
 
-			mmdc: mmdc@21b0000 {
+			memory-controller@21b0000 {
 				compatible = "fsl,imx6sl-mmdc", "fsl,imx6q-mmdc";
 				reg = <0x021b0000 0x4000>;
 				clocks = <&clks IMX6SL_CLK_MMDC_P0_IPG>;

arch/arm/boot/dts/imx6sx.dtsi

@@ -1017,7 +1017,7 @@ i2c3: i2c@21a8000 {
 				status = "disabled";
 			};
 
-			mmdc: mmdc@21b0000 {
+			memory-controller@21b0000 {
 				compatible = "fsl,imx6sx-mmdc", "fsl,imx6q-mmdc";
 				reg = <0x021b0000 0x4000>;
 				clocks = <&clks IMX6SX_CLK_MMDC_P0_IPG>;

arch/arm/boot/dts/imx6ul.dtsi

@@ -914,7 +914,7 @@ i2c3: i2c@21a8000 {
 				status = "disabled";
 			};
 
-			mmdc: mmdc@21b0000 {
+			memory-controller@21b0000 {
 				compatible = "fsl,imx6ul-mmdc", "fsl,imx6q-mmdc";
 				reg = <0x021b0000 0x4000>;
 				clocks = <&clks IMX6UL_CLK_MMDC_P0_IPG>;