arm64: dts: imx8m: Add fsl,ddr-pmu to ddrc nodes

The imx8m-ddrc driver can dynamically measure memory usage using ddr
pmu. Enable this by adding a "fsl,ddr-pmu" phandle reference.
Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>

arch/arm64/boot/dts/freescale/imx8mm.dtsi

@@ -970,9 +970,10 @@ ddrc: memory-controller@3d400000 {
 				 <&clk IMX8MM_DRAM_PLL>,
 				 <&clk IMX8MM_CLK_DRAM_ALT>,
 				 <&clk IMX8MM_CLK_DRAM_APB>;
+			fsl,ddr-pmu = <&ddr_pmu>;
 		};
 
-		ddr-pmu@3d800000 {
+		ddr_pmu: ddr-pmu@3d800000 {
 			compatible = "fsl,imx8mm-ddr-pmu", "fsl,imx8m-ddr-pmu";
 			reg = <0x3d800000 0x400000>;
 			interrupts = <GIC_SPI 98 IRQ_TYPE_LEVEL_HIGH>;

arch/arm64/boot/dts/freescale/imx8mn.dtsi

@@ -837,9 +837,10 @@ ddrc: memory-controller@3d400000 {
 				 <&clk IMX8MN_DRAM_PLL>,
 				 <&clk IMX8MN_CLK_DRAM_ALT>,
 				 <&clk IMX8MN_CLK_DRAM_APB>;
+			fsl,ddr-pmu = <&ddr_pmu>;
 		};
 
-		ddr-pmu@3d800000 {
+		ddr_pmu: ddr-pmu@3d800000 {
 			compatible = "fsl,imx8mn-ddr-pmu", "fsl,imx8m-ddr-pmu";
 			reg = <0x3d800000 0x400000>;
 			interrupts = <GIC_SPI 98 IRQ_TYPE_LEVEL_HIGH>;

arch/arm64/boot/dts/freescale/imx8mq.dtsi

@@ -1511,9 +1511,10 @@ ddrc: memory-controller@3d400000 {
 				 <&clk IMX8MQ_DRAM_PLL_OUT>,
 				 <&clk IMX8MQ_CLK_DRAM_ALT>,
 				 <&clk IMX8MQ_CLK_DRAM_APB>;
+			fsl,ddr-pmu = <&ddr_pmu>;
 		};
 
-		ddr-pmu@3d800000 {
+		ddr_pmu: ddr-pmu@3d800000 {
 			compatible = "fsl,imx8mq-ddr-pmu", "fsl,imx8m-ddr-pmu";
 			reg = <0x3d800000 0x400000>;
 			interrupt-parent = <&gic>;