dt-bindings: imx8m-ddrc: Add fsl,ddr-pmu property

Like other devfreq drivers imx8m-ddrc can measure memory bandwith usage.
This is only enabled if a link is provided to the imx8m ddr pmu.

This is referenced with a custom fsl,ddr-pmu property because
devfreq-events was deprecated.
Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Acked-by: Chanwoo Choi <cw00.choi@samsung.com>

Documentation/devicetree/bindings/memory-controllers/fsl/imx8m-ddrc.yaml

@@ -49,6 +49,10 @@ properties:
   operating-points-v2: true
   opp-table: true
 
+  fsl,ddr-pmu:
+    description: Phandle of PMU node
+    $ref: "/schemas/types.yaml#/definitions/phandle"
+
 required:
   - reg
   - compatible
@@ -60,6 +64,7 @@ additionalProperties: false
 examples:
   - |
     #include <dt-bindings/clock/imx8mm-clock.h>
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
     ddrc: memory-controller@3d400000 {
         compatible = "fsl,imx8mm-ddrc", "fsl,imx8m-ddrc";
         reg = <0x3d400000 0x400000>;
@@ -70,3 +75,10 @@ examples:
                  <&clk IMX8MM_CLK_DRAM_APB>;
         operating-points-v2 = <&ddrc_opp_table>;
     };
+
+    ddr_pmu: ddr-pmu@3d800000 {
+        compatible = "fsl,imx8mm-ddr-pmu", "fsl,imx8m-ddr-pmu";
+        reg = <0x3d800000 0x400000>;
+        interrupt-parent = <&gic>;
+        interrupts = <GIC_SPI 98 IRQ_TYPE_LEVEL_HIGH>;
+    };