arm64: dts: imx8dxl-ss-ddr: change ddr_pmu0 compatible

i.MX8DXL's ddr pmu has port/channel filter capabilities, but it still is
compatible with "fsl,imx8-ddr-pmu". This will change the compatible.
Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8dxl-ss-ddr.dtsi

@@ -4,6 +4,6 @@
  */
 
 &ddr_pmu0 {
-	compatible = "fsl,imx8-ddr-pmu";
+	compatible = "fsl,imx8dxl-ddr-pmu", "fsl,imx8-ddr-pmu";
 	interrupts = <GIC_SPI 71 IRQ_TYPE_LEVEL_HIGH>;
 };